To easily perform air bleed from a path in which variable capacity control of a hydraulic pump-motor is carried out.

An air bleed regulating valve 59 is provided at a connector 57, and when air is entered into a path from a drain tank 53 to a power unit 54 and the connecter 57, constituting a pressure accumulating means 52 for controlling the tilt angle of a swash plate 32 of the hydraulic pump-motor, air bleed is performed by operating clamping bolts easily and even after assembling, oil-pumping up is constantly performed by plural (for example, three) pumping means 55a, 55b, 55c of the power unit 54, and an increase in the burden on a pumping means 55 is suppressed to make possible the pressure accumulation of a regulating accumulator 51 in a short time.