A rotary fluid machine is provided in which a rotating shaft (113) fixed to a rotor (41) is rotatably supported on a fixed shaft (102) fixed to a casing (11), sliding surfaces of the fixed shaft (102) and the rotating shaft (113) are lubricated by a first pressurized liquid-phase working medium, and sliding surfaces of the rotor (41) and a vane (48) are lubricated by a second pressurized liquid-phase working medium. By setting the pressure of the first pressurized liquid-phase working medium, which is supplied from an eleventh water passage (W11), comparatively low and setting the pressure of the second pressurized liquid-phase working medium, which is supplied from a first water passage (W1), comparatively high, wasteful leakage of the liquid-phase working medium past the sliding surfaces of the fixed shaft (102) and the rotating shaft (113), where a comparatively small load is applied, can be prevented while enabling the sliding surfaces of the rotor (41) and the vane (48), where a large load is applied, to be reliably lubricated with a high pressure liquid-phase working medium.