PURPOSE: To provide a variable diameter wheel capable of transmitting a force by arranging two facing discs with their positions changeable in the opposite direction to the direction of their rotary shaft, thinning each plate from one disc toward the other disc, and coupling such plates laid in line so that their positions are changeable simultaneously.

CONSTITUTION: A plate 9 is guided between two discs 2 and 3 facing each other and is made slidable from inside to outside or vice versa. The positions of the two discs 2 and 3 are made changeable in the opposite direction to the direction of their rotary shaft 6, and the plate 9 is thinned in the circumferential direction from one disc 2/3 to the other 3/2, and such plates 9 laid in line are arranged so that their positions are changeable simultaneously. Thereby a variable diameter wheel 1 is accomplished which can be used to transmit the force due to coupling in terms of force or shape.