a thermal cooker in the present invention , as shown in fig1 - 3 , comprises an outer cooker 1 having an opening 10 in the top and two opposite grips 11 extending out from an upper wall , an insulating disc 2 made of a heat non - conductive material inner and placed on an inner bottom of the outer cooker 1 , and an cooker 3 for boiling food and to be placed on the insulating disc 2 and having an upper lid 30 and a hole 31 each formed in a semi - round projection on two opposite upper edges and a large semi - circular handle 32 with both ends hooked in the two holes 31 , 31 . the thermal cooker also comprises a sealing lid unit 4 closing the opening 10 of the cooker 1 . the sealing lid unit 4 consists of a lid 40 , a lower cap 41 , an annular sealing gasket 42 , an air seal 43 , and a top cap 44 . the lid 40 has a recess 400 in the center portion , a through hole 401 in the center of the recess 400 , four air holes 402 spaced equally around the through hole 401 , an annular fitting wall 403 projecting down from the bottom of the recess 400 , a circumferential upper edge 404 , two annular wails 405 . 406 extending down from the upper edge 404 , an annular groove 407 formed between the two annular walls 405 , 406 . the lower cap 41 fits around the annular wall 403 , having two air holes 41 , 41 . the annular sealing gasket 42 engages the annular groove 407 , made of a soft rubber and having a flange 420 in an annular intermediate portion . the air seal 43 is made of soft rubber and fits in the recess 400 , having an inverted mushroom shape and extending down from a bottom to fit through the center hole 401 and two inclined connecting rods 431 , 432 extending upward . the top cap 44 has a swelled top , two opposite slots 441 , 442 in the swelled top , and a circumferential vertical surface 440 . in assembling , first , the lower cap 41 is pushed to engage the annular fitting wall 403 , and next the annular sealing gasket 42 is placed to engage the annular groove 407 . then the block 430 of the air seal 43 is inserted through the through hole 401 , stopping under the hole 401 , and letting the air seal 43 close the four air holes 402 . after that , the slots 441 . 442 of the top lid 44 are managed to pass through by the two inclined rods 431 , 432 . letting the top lid 44 fits exactly in the recess 400 on the air seal 43 and then the top lid 44 is to be welded with the lid 40 . thus the sealing lid unit 4 is completely assembled together . in using , as shown in fig3 and 4 , first , food to be cooked is to be placed in the inner cooker 3 and to be boiled properly , and then the inner cooker 3 is picked up by holding the handle 32 . then the inner cooker 3 is to be put on the insulating disc 2 in the outer cooker 1 , and the sealing lid unit 4 is to be put to close on the opening 10 of the outer cooker 1 . then a separate air sucking pump a is placed on the recess 400 , and then a air rod a1 of the air sucking pump a is pulled up to suck out the in the outer cooker 1 . the air in the outer cooker 1 will flow orderly through the two air holes 410 of the lower cap 41 , the four air holes 402 , through a gap between the air seal 43 and the recess 400 , the two slots 441 . 442 , and finally into the air sucking pump a . if the pulling rod a1 is pushed down , as shown in fig4 the air coming from the outer cooker 1 in the air - sucking pump a may be exhausted out of an outlet hole a10 of the pushing rod a1 . thus the air in the outer cooker 1 can be quickly sucked out air to become vacuum by operating the air sucking pump a . then pressure inside of the cooker 1 turns out to be very lower than that outside the cooker 1 i . e . the atmosphere , the sealing gasket 42 is pushed by open air to close tightly the upper circumference of the outer cooker 1 , not allowing open air to flow into the outer cooker 1 . in addition , the air seal 43 is pressed by the pressure of open air ( atmosphere ) to close up tightly the four air holes 402 of the recess 400 . so once the outer cooker 1 becomes vacuum , it may be kept such vacuum , with impossibility of air flowing into the outer cooker 1 . the inner cooker 3 is located on the separating disc 2 , separated by the insulating disc 2 from the bottom of the outer cooker 1 so that the heat of the food in the inner cooker 3 cannot be conducted to the outer cooker , nor to the vacuum empty interior of the outer cooker 1 , allowing the food therein being kept heated to get cooked for a long period of time . if the food cooked in the inner cooker 3 is needed to be taken out , as shown in fig5 either of the two connecting rods 431 , 432 is moved inward in the slots 441 , 442 of the top cam 44 , letting a gap formed between the air seal 43 and the groove 400 . then open air may immediately flow through the gap and the slots 441 , 442 , the four air holes 402 , the two air holes 410 , 410 and then into the outer cooker 1 until the pressure inside the outer cooker 1 and the pressure of the open air become balanced , allowing the sealing gasket 42 not closely engage the outer surface of the outer cooker 1 so that the sealing lid unit 4 may be taken off . then the food in the inner cooker 3 can be taken out for a meal . as can be seen from the above description , this vacuum thermal cooker has advantages as listed below . 1 . air in the outer cooker can be sucked out almost completely to become vacuum , enabling the heat of the food in the inner cooker kept very long for cooking the food well - done or keeping the food warm very long by vacuum condition of the interior of the outer cooker . 2 . the inner cooker 3 can be almost completely isolated from open air so that the heat of the food may not decrease easily , and the food does not need to be warmed once again in time of meal .