A control mechanism for a stepless transmission is a control mechanism connected to a manipulation lever in a stepless transmission and disposed outside a housing of the transmission. The control mechanism includes: a) a piston rod connected to the manipulation lever; b) a piston provided on the piston rod coaxially with the piston rod; c) a cylinder case provided with a cylinder adapted to house the piston rod and the piston such that the piston rod and the piston are displaceable in an axial direction, the piston and the cylinder forming a first fluid chamber to be supplied with a hydraulic fluid for withdrawing the piston rod from the cylinder and a second fluid chamber to be supplied with the hydraulic fluid for introducing the piston rod into the cylinder; d) a spring adapted to bias the manipulation lever in a neutral direction coaxially with the piston rod; e) a proportional pressure control valve adapted to selectively supply the hydraulic fluid to the first fluid chamber or the second fluid chamber, the proportional pressure control valves being mounted to the cylinder case; and f) a pivot shaft adapted to support the cylinder case oscillatably with respect to the housing.