A switch valve structure of a fluid machine (10) having a pump mode to operate as a compressor and a motor mode to operate as an expander is disclosed. In pump mode, a communication path (106) between a working chamber (V) and a high-pressure chamber (104) is closed, while in motor mode, the communication path (106) is opened by a valve unit (107d). The valve unit (107d) is includes a spool portion (117) sliding in the direction substantially perpendicular to the surface to which the communication path (106) opens and a valve portion (127) arranged at the forward end of the spool portion (127) and sliding with the spool portion (117) thereby to open/close the communication path (106). A swivel mechanism (137) is interposed between the spool portion (117) and the valve portion (127) to tilt the sliding axis of the valve portion (127) at an arbitrary angle with respect to the sliding axis of the spool portion (117).