PURPOSE: To smooth operation of a continuously variable transmission including a variable speed ring which surrounds conical surfaces of a plurality of conical rollers performing planetary movement, frictionally engages with them and is axially movable, by providing a cam mechanism moving the variable speed ring to the low speed side with the increase of load torque.

CONSTITUTION: In an electric motor truck, a friction type continuously variable transmission 2 is directly coupled with an output shaft of a DC motor 1 and output rotation of the variable speed change gear 2 is transmitted to driving wheels from an output shaft 4. In the friction variable speed change gear 2, a plurality of conical rollers 7 performing planetary movement are interposed between an input disc 5 rotated by the motor 1 and an output disc 6 connected to the output shaft 4, and a variable speed ring 8 which surrounds the conical surfaces of the rollers 7 and frictionally engages with them is axially moved to perform the speed change. In this case, a cam mechanism 9 for moving the variable speed ring 8 to the low speed side with the increase of load torque is attached. The cam mechanism 9 is constituted so that a cam driven piece 13 supported with a speed change gear casing 11 is brought into slide contact with a cam 12 provided on the variable speed ring 8.