A compressor includes a screw rotor and a gate rotor. The screw rotor has a plurality of spirally extending groove portions disposed radially outwardly from the center axis of the screw rotor. The gate rotor has a plurality of tooth portions circumferentially arranged on an outer circumference to engage the groove portions. Preferably, an inclination angle of a groove portion side face contacting the tooth portions is inclined relative to a circumferential direction of the gate rotor varies. Alternatively a first plane contains the screw rotor center axis, a second plane orthogonally intersects the screw rotor center axis, a third plane orthogonally intersects the first and second planes, the gate rotor center axis is on the third plane, and the tooth portions do not overlap the first plane as viewed orthogonally relative to the third plane.