To lighten the burden on a high-pressure side of seal and to facilitate management for gaps between a rotor chamber and rotor end faces.

This fluid machine comprises casings 7, 9 having the rotor chamber 11, a suction port 13 and a discharge port 15; rotors 3, 5 having rotor bodies 31, 33 housed in the rotor chamber 11; seals 17 preventing fluid leakage from the rotor chamber 11; and decompression parts 23 formed in high-pressure side end parts of the rotor bodies 31, 33. The decompression part 23 comprises a recessed part 61 formed from the end face of the rotor body 31, 33 to the axial inner side; a projecting part 63 on the casing 7 side opposite to the recessed part 61; and a decompression member 65 fixed in the recessed part 61, decompressing fluid moving through a gap facing the projecting part 63.