To provide a structure of a moderating mechanism for moderating sudden output change during shifting in a hydraulic continuously variable transmission, operating to moderate output change against sudden operation of a transmission operation tool.

In a housing 33 forming an oil reservoir, a hydraulic pump 37, a hydraulic motor 36, and a center section 38 are housed, at least one of the hydraulic pump and the hydraulic motor is of a variable displacement type, and the center section forms closed oil paths between the hydraulic pump and the hydraulic motor. The hydraulic continuously variable transmission 25 is composed of the hydraulic pump 37, the hydraulic motor 36, and the center section 38 and shiftable by changing a flow rate in the oil paths by operation of the transmission operation tool 26. A drain oil path is communicated with the closed oil paths through an openable/closable leak valve 68, the leak valve 68 is opened against the sudden operation of the transmission operation tool 26, and hydraulic oil in the closed oil paths is leaked to the oil reservoir.