To provide a speed change gear capable of efficiently transmitting power even in a constitution changing a diameter of a pulley.

A belt winding part of a pulley 10 is formed by a pulley belt 20 having many teeth 20a, so as to transmit turning force by a transmitting pulley 30 having many teeth 30a meshed with this pulley belt, in this way, power can be efficiently transmitted by meshing of each tooth 20a, 30a. Here, one end of the pulley belt 20 is fixed to the belt winding part, and the other end side thereof is inserted in an unfixed condition to an inner side of the belt winding part, so as to change a peripheral length of the pulley belt 20 also change it by stages in each prescribed pitch of the teeth 20a, in this way, the teeth 30a of the transmitting pulley 30 and the teeth 20a of the pulley belt 20 can be always surely meshed with each other even by changing a speed.