To positively ensure sliding contact face sealing performance immediately after starting without increasing friction in the whole area of operation.

A hydraulic continuously variable transmission is provided with pressure receiving parts 23a, 24a receiving pump discharge pressure side high pressure and suction side low pressure to seal the sliding contact faces of a cylinder block 11 and a port block 22 of a hydraulic motor 1, and reversibly rotated according to an oil pressure supply direction from a hydraulic pump 3 to the hydraulic motor 1. The effective pressure receiving area of the forward side pressure receiving part 23a is made small so as to maintain oil pressure balance at the time of high pressure, and the effective pressure receiving area of the reverse side pressure receiving part 24a is set large so as to maintain oil pressure balance at the time of low pressure. A delay means is provided to build up the circuit pressure of the reverse side pressure receiving part 24a first at the time of forward starting. Oil pressure balance is maintained by pressing force of the reverse side pressure receiving part 24a to prevent leakage, and after pressure is sufficiently built up, oil pressure balance is maintained by the forward side pressure receiving part 23a.