To provide a fluid machine capable of preventing a vane from separating from a piston without pressing the vane composed as a different body from the piston against the piston inward in the radial direction.

The fluid machine has a rotary mechanism 2A including a cylinder 21, an eccentric part 32, and the piston 22. A working chamber 23 formed between an inner circumferential surface of the cylinder 21 and the piston 22 is partitioned into an intake side 23A and a discharge side 23B by the vane 24. The vane 24 has a pivot 24a at an end on the cylinder 21 side thereof. The cylinder 21 has a bearing 21a supporting the pivot 24a rotatably, and a vane groove 22a to which the vane 24 is inserted reciprocatably is provided for the piston 22.