A fluid machine (201) includes: a compression mechanism (2) for compressing a working fluid; an expansion mechanism (4) for expanding the working fluid and for recovering mechanical power from the expanding working fluid; a shaft (5) for coupling the compression mechanism (2) and the expansion mechanism (4) and for transferring the mechanical power recovered by the expansion mechanism (4) to the compression mechanism (2); and a closed casing (1) for accommodating the compression mechanism (2), the shaft (5) and the expansion mechanism (4), and having an internal space into which the working fluid that has been compressed by the compression mechanism (2) is discharged. A refrigerant passage space (7) through which a refrigerant to be drawn into the expansion mechanism (4) passes is formed between an expansion chamber of the expansion mechanism (4) and the internal space of the closed casing (1).