reference will now be made in detail to various embodiments of the present invention ( s ), examples of which are illustrated in the accompanying drawings and described below . while the invention ( s ) will be described in conjunction with exemplary embodiments , it will be understood that present description is not intended to limit the invention ( s ) to those exemplary embodiments . on the contrary , the invention ( s ) is / are intended to cover not only the exemplary embodiments , but also various alternatives , modifications , equivalents and other embodiments , which may be included within the spirit and scope of the invention as defined by the appended claims . referring to fig3 , an embodiment of the present invention includes a connector 3 converting rotational force of a motor 1 into straight movement force ; connecting springs 7 having an end connected to an upper wedge 5 and the other end connected to connector 3 ; and support members 9 extending from connector 3 toward upper wedge 5 . the connecting springs 7 are bolted to the upper wedge 5 . in the embodiment of fig3 , two connection springs 7 are provided . each connecting spring 7 includes an elongated strip portion having two opposite surfaces . as illustrated , one of the surfaces faces the upper wedge 5 , and the other surface 13 faces away from the upper wedge 5 . one support member 9 is provided on the surface 13 to support the spring 7 . according to embodiments , the moving angle of upper wedge 5 is larger than the mounting angle of motor 1 and the difference is set within 10 °. in the foregoing configuration , the upper wedge 5 is configured to move along its inclined surface 15 whereas the connecting spring 7 moves along the axial direction of the motor 1 , which has to do with mounting angle of the motor 1 . as such , with reference to a reference plane or line , the moving angle of upper wedge 5 is the same as the angle of the inclined surface supported by a roller 11 ; and the mounting angle of motor 1 is the same as the angle of the straight movement by connector 3 and the moving angle of the spring 7 . referring to fig4 , “ x ” is the reference plane or line , the moving angle of upper wedge 5 relative to the brake disc is a , and the mounting angle of motor 1 is b . according to embodiments , the difference between a and b is within 10 °. in this configuration , if the moving angle of upper wedge 5 is set too much larger than the mounting angle of motor 1 , the effect that connecting spring 7 is supported by support member 9 ; therefore , it is preferable that the difference is within 10 °. in the foregoing configuration , the motor 1 operates and the connecting springs 7 apply pressing force to upper wedge 5 at the angle b , which moves the upper wedge 5 at the angle a to perform front braking . then , the connecting spring 7 may be forced in the opposite direction from the upper wedge 5 , which could cause buckling of the spring 7 but for the support members 9 . however , the support members 9 prevents such buckling from occurring . thus , the connecting springs 7 can smoothly push upper wedge 5 with sufficient stiffness . further , as the possibility of buckling of connecting spring 7 is reduced , as described above , connecting springs 7 can be made of a more flexible material to flexibly bend in the rear braking , as described above , and smoothly pull upper wedge 5 by making connecting springs more flexible , and accordingly , it is possible to implement stable and smooth rear braking . fig5 is a view showing another embodiment of the present invention , the moving angle of upper wedge 5 is set to be the same as the mounting angle of motor 1 , and other than support members 9 provided to connector 3 , upper wedge 5 is further provided with additional support members 13 extending toward connector 3 to support the surfaces facing upper wedge 5 of connecting springs 7 . in this embodiment , since support members 9 and additional support members 13 are formed in a size to overlap each other , with connecting springs 7 therebetween , there is no section at any one side over the entire length which is not supported by support members 9 or additional support members 13 in connecting spring 7 . as described above , when the moving angle of upper wedge 5 is set to be the same as the mounting angle of motor 1 , connecting springs 7 may buckle toward upper wedge 5 . accordingly , connecting springs 7 are supported by additional support members 13 to prevent the buckling . fig6 illustrates bending of a connecting spring 7 while being supported by the support members 9 and additional support members 13 . the support members 9 and additional support members 13 appropriately support connecting springs 7 to prevent them from buckling in the front braking , and connecting springs 7 smoothly deform and upper wedge 5 smoothly moves in the rear braking , such that it is possible to achieve smooth and stable operability in the rear braking . the foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description . they are not intended to be exhaustive or to limit the invention to the precise forms disclosed , and obviously many modifications and variations are possible in light of the above teachings . the exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application , to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention , as well as various alternatives and modifications thereof . it is intended that the scope of the invention be defined by the claims appended hereto and their equivalents .