In a Roots displacement fluid machine (5) comprising rotors (15, 17) meshed with each other in a tooth trace (57, 59) formed in parallel to a rotating central axis, and a casing (13) having a rotor chamber (33) rotatably receiving the rotors (15, 17), a fluid inlet port for a fluid and a fluid outlet port, an inclined surface (67) forming an angle &thgr; with respect to an opposing surface (65) of the rotor chamber (33) is disposed at least in a tip end of the end portion of the rotor (15), and a gap (69) is formed with respect to the opposing surface (65).
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