referring to fig1 a mounting device of 3 - point link type for an implement is arranged at a rear of an agriculture tractor . the device includes a top link 18 and lower links ( not shown ). an implement mounting hitch a according to the invention is mounted at the rear end of the mounting device of the 3 - point link type . the implement mounting hitch a comprises a frame 1 , a pair of lower engagement hooks 2 , an upper engagement hook 3 , a pair of hooks 5 associated to the hooks 2 , a hitch plate 8 ( fig5 ) and lower link pins 6 . the top link 18 of the mounting device is pivotably connected at the rear end thereof to the upper end of the frame 1 through a pin . the lower links are fitted at the rear ends thereof to the lower link pins 6 of the hitch a . the one top link 18 and a pair of said lower links support three points of the hitch a and is adapted to raise and lower it by a hydraulic unit provided in the tractor . the vertical movement of the mounting hitch a can cause engagement of an upper pin 39 , which is provided at a top link mast 13 ( connected to the top link mast 12 ) in an implement b , with the engagement hook 3 at the upper end of the frame 1 . when the mounting hitch a is raised after this engagement , the implement b is drawn toward the mounting hitch a , so that lower link pins 7 of the implement are fitted into concave portions 2a of the hooks 2 after pushing away from hooks 5 . then , the hooks 5 which are biased by springs return to an initial position , in which the pins 7 are fitted into concave portions 5a provided at the hooks 5 , so that the implement b is completely mounted to the mounting hitch a . in order to accomplish the above engagement , the upper engagement hook 3 is projected upwardly from the frame 1 . each lower hook 2 of the mounting hitch a opens toward the lower link pin 7 provided at a lower link hinge 15 in the implement b . at 4 is indicated a release handle or lever for releasing the engagement of the hook 5 . in order to release the implement b from the mounting hitch a , the release handle 4 is operated to a release position to open the hook 5 . then , the mounting hitch a is lowered to release the engagement of the lower engagement hooks 2 and the lower link pins 7 , and then , the upper engagement hook 3 is released from the upper pin 39 . thereafter , the tractor is moved forwardly . the position of the lower link pins 7 in the implement b are so determined that they may be aligned on a same line as a drive shaft 17 ( fig6 and 7 ) supported in the hitch a when the pins 7 are fitted into the engagement concave portions 2a at the lower engagement hook 2 to mount the implement b . in fig1 at 11 is indicated a gearbox for the implement ( e . g ., a rotary plow ). at 16 is indicated a cover of the rotary plow . at 24 is indicated a main beam . as shown in fig3 the frame 1 is of inverted u - shape , and the upper engagement hook 3 is rigidly fixed to an upper central portion of the frame 1 . the hooks 5 are supported by lower link pins 6 , which is rigidly fixed to the opposite lower ends of the frame 1 . as shown in fig4 each lower link pin 6 is fixed to the lower engagement hook 2 and a bent reinforcement plate 14 . each hook 5 is rigidly connected to the release lever 4 ( fig1 ) and is supported by an outer periphery of a cylindrical support shaft , of which inner periphery is supported by the lower link pin 6 . a spring ( not shown ) is connected to each release lever 4 so that the lever 4 may be held by the elastic force thereof either in a release position or an engagement position for holding the lower link pin 7 . the hitch plate 8 is illustrated also in fig5 . the drive shaft 17 is supported by the hitch plate 8 in a manner as illustrated in fig6 and 7 . the rear and side view of the hitch plate 8 are illustrated in fig8 and 9 , respectively . an elastical holder plate 25 is illustrated in fig1 and 11 . the holder plate 25 includes a hole for a bolt as illustrated in fig1 . bearings for the drive shaft and bearing cases are constructed as illustrated in fig6 , 13 and 14 . the drive shaft 17 is constructed as illustrated in fig1 and 16 . as described before , the implement b is mounted by engaging the upper and lower engagement hooks 2 and 3 of the hitch a with the upper pin 39 and the lower link pins 7 of the implement b . simultaneously with this engagement , the drive shaft 17 connected to a pto shaft of the tractor is automatically coupled to an input shaft of the rotary gear box 11 ( fig1 ). a universal joint 26 ( fig1 ) covered by a universal joint cover 32 is projected rearwardly from the pto shaft , and is coupled to the drive shaft 17 which is supported by the plate 8 of the hitch a through the bearings . as shown in fig7 the drive shaft 17 is disposed at a central position of the hitch plate 8 , and is so adapted that a coupling member 9 ( fig6 ) on the drive shaft 17 is automatically coupled with a coupling member 21 on the input shaft of the implement b . simultaneously with said mounting of the implement b . bolts 40 ( fig7 ) are inserted into the holes provided at the lower engagement hooks 2 and is screwed into threaded apertures 8c formed in end plates 8b provided at the ends of the hitch plate 8 , so that , as shown in fig8 and 9 , the hitch plate 8 is fixed between a pair of the lower engagement hooks 2 by the bolts 40 . when viewed in the forward direction , ( e . g ., as fig3 ), the coupling members 9 and 21 ( fig1 ) are coupled to a central position of the hitch plate 8 , which is vertically aligned with the engaged upper hook 3 ( fig1 ) and the upper pins 39 . the hitch plate 8 is provided at the central position thereof with a hole 8d ( fig8 ) for passing the drive shaft 17 therethrough , and is also provided at lengthwise opposite sides of the hole 8d with a pair of vertically long apertures 8a for vertically movably supporting a drive shaft bearing 10 ( fig6 ). the universal joint 26 ( fig1 ) is splined to the front end of the drive shaift 17 . the drive shaft 17 is provided at the rear end thereof with the coupling 9 , which engages the coupling 21 at the front end of the input shaft of the implement to transmit a power thereto . even when the drive shaft 17 is coupled with the input shaft of the implement , there are often radial deviation between the two shafts . in order to coaxially positioning them at initial rotation thereof , the drive shaft 17 is radially movably supported , as described below . the drive shaft 17 is supported by the bearing 18 as well as a bearing 20 , both of which are movable to some extent . the bearing case 10a of the bearing 10 is supported by bolts 23 inserted into said long apertures 8a in the hitch plate 8 . as shown in fig5 a wave - shaped washer 22 is interposed between the bearing case 10a and each bolt 23 . the washer 22 is softly held between the bearing case 10a and the bolt 23 so that the bearing case 10a can move vertically along the long aperture 8a . further , the bearing 20 supporting the rear portion of the shaft 17 has a bearing case 20a which is biased by the elastic holder plates 25 . as shown in fig7 the plates 25 are disposed at horizontally opposite sides of the case 20a , so as to elastically holding the rear end of the shaft 17 at the regular central position . each holder plate 25 is formed by a plate spring and is fixed at it upper and lower ends by the bolts to support members 19 , which are fixed to the hitch plate 8 , as shown in fig6 . this structure permits radial movement of the bearing 20 to some extent . therefore , even when the coupled members 9 and 21 are radially deviated from each other , this deviation will be corrected by the radial movement of the bearing 20 , which is permitted by the elastic deflection of the holder plates 25 . as shown in fig6 the coupling members 9 and 21 are provided with axial concave portions and convex portions to be alternately fitted into each other . in the mounting operation , in which the implement b is drawn toward the mounting hitch a , the convex portions of both of the coupling members 9 and 21 may contact each other , in which case either of them should retreat . in order to perform this retreat , the coupling member 9 and the bearing 20 fitted therearound are axially movable on the drive shaft 17 . further , axially stacked belleville springs 7 are interposed around the shaft 17 and between the coupling member 9 and the bearing 10 so as to return the forwardly retreated member 9 and the bearing 20 to the initial position . as illustrated in fig1 and 16 , the forward end of the drive shaft 17 has a nearly hexagonal section and is provided with spline teeth . that is ; the forward end of the shaft 17 has a section same as that of a conventional input shaft of an implement , so that the shaft 17 may be connected to the universal joint ( fig1 ) of the tractor . first of all , the implement b can be facilely mounted and released by lifting or lowering the implement b with the operator staying on the operator &# 39 ; s seat . further , the drive shaft 17 and the input shaft of the implement b can be coupled simultaneously with the mounting of the implement without manual operation for coupling the universal joint , which is required in the conventional structure , after the mounting of the implement . even if there is a radial deviation or relative inclination between the drive shaft 17 and the input shaft of the implement , the coupling members 9 and 21 are automatically aligned with each other and smoothly coupled together when the implement b is mounted to the hitch a . when mounted , the implement b is reliably fixed to the hitch a by the upper and lower hooks 2 and 3 , so that it can be mounted stably without generating vibration and noises , resulting in long durability . although the invention has been described in its preferred form with a certain degree of particularity , it is understood that the structure of the preferred form may be changed in the details of construction , and that the combination and arrangement of parts may be modified without departing from the spirit and scope of the invention as hereinafter claimed .