A displacement type fluid machine comprising at least one suction port, at least one discharge port, a displacer having an outer wall surface, a rotating shaft around a center of rotation of which said displacer orbits, and a cylinder having an inner wall surface within which said displacer is provided and having a plurality of extrusions extruded inwardly of said cylinder, wherein the inner and outer wall surfaces are shaped such that one space would be provided between the inner wall surface of said cylinder and the outer wall surface of said displacer if a center of said displacer is located on the center of rotation of said rotating shaft, and a plurality of spaces are formed between the inner wall surface and the outer wall surface when a positional relationship between said displacer and said cylinder is located on a center of gyration,
- wherein the curves of the inner wall surface of said cylinder and the outer wall surface of said displacer are formed so that a shaft angle .theta.c of the process from the suction completion to the discharge completion in said plurality of spaces satisfies the following algorithm:
- (((N-1)/N.multidot.360.degree.)<.theta.c.ltoreq.360.degree.,
- wherein, N is the number of the extrusions extruded inwardly of said cylinder.