To provide a screw type fluid machine, by which a bypass port and a discharge port are prevented from being connected to each other via a tooth space as to an optional bypass port position and fluids with different preset pressures can be obtained from the bypass port and the discharge port individually, provided with a bypass port.

This fluid machine is provided with a male rotor 6 and a female rotor 9, which are engaged with each other and rotate around parallel axes, and a casing 1 storing the both rotors 6, 9, while the casing 1 is provided with a suction port, a discharge port 2, and a bypass port 14 communicated with a tooth space during a compression stroke. In the discharge end face part of the casing 1, a bypass passage 4 and an opening/closing mechanism (timing gears 12, 13) opening/closing the bypass passage 4 are arranged, and the bypass port 14 is connected to the bypass passage 4 via the opening/closing mechanism, which is constructed so as to cut off communication between the bypass port 14 and the bypass passage 4 just before the discharge port 2 is communicated with the tooth space.