To reduce energy used in operation of a transmission by a shifting actuator for preventing an increase in energy consumed by the shifting actuator according to an increase in capacity of the transmission, even when the capacity of the transmission is enhanced.

In a stage shifting device 10, a thrust spring 20 energizes a movable sheave 257 toward a fixed sheave 253 side in the axial direction with thrust DF matching a tension TF of a V belt 211, and the outer diameter of a winding region of a pulley groove 262, with which the V-belt 211 is brought into pressure contact, is varied to follow an outer diameter change in the winding region in the pulley groove 16 by the shifting operation of the shifting actuator 100. A counter spring 18 energizes a movable sheave 207 toward a fixed sheave 203 in the axial direction with a counter force CF matching the thrust DF of the thrust spring 20.