Rotary type fluid machine includes a casing 7, a rotor 31 and a plurality of vane-piston units U1-U12 which are disposed in a radiate arrangement on the rotor 31. Each of the vane-piston units U1-U12 has a vane 42 sliding in a rotor chamber 14 and a piston 41 placed in abutment against a non-slide side of the vane 42. When it functions as an expanding machine 4, the expansion of a high pressure gas is used to operate the pistons 41 thereby to rotate the rotor 31 via vanes 42 and the expansion of a low pressure gas caused by a pressure reduction in the high pressure gas is used to rotate the rotor 31 via the vanes 41. On the other hand, when it functions as a compressing machine, the rotation of rotor 31 is used to supply a low pressure air to the side of pistons 41 via vanes 42 and further, the pistons 41 are operated by the vanes 42 to convert the low pressure air to the high pressure air. Thus, a rotary type fluid machine having expanding and compressing functions, with the merits belonging to the piston type and the merits belonging to the vane type, can be provided.