To provide a capacity control system for a variable capacity motor to perform a slow motion without varying a command to a minimum pressure (a low speed) even when a command for a maximum pressure (a high speed) is outputted to a solenoid proportional valve for capacity control to effect high speed operation.

Control is effected by a directional control valve 3 by which the secondary pressure of a remote control valve 5 having an operation pressure forming the secondary pressure of the remote control valve 5 and capacity is variable in a way that the secondary pressure of a solenoid proportional valve 4 for controlling capacity forms an operation pressure. In a so formed variable capacity hydraulic motor 1, the secondary pressure of the remote control valve 5 forms the primary pressure of the solenoid proportional valve 4 for controlling capacity, and the operation pressure of the directional control valve 3 and the primary input of the solenoid proportional valve 4 for controlling capacity are rendered equal to each other and capacity of the variable capacity hydraulic motor 1.