A screw compressor includes a low pressure stage compressor body; a high pressure stage compressor body that further compresses a compressed air compressed by the low pressure stage compressor body; pinion gears for example, respectively, provided on, for example, a male rotor of the low pressure stage compressor body and, for example, a male rotor of the high pressure stage compressor body; a motor; a bull gear for example, provided on a rotating shaft of the motor; and an intermediate shaft supported rotatably and provided with a pinion gear, which meshes with the bull gear, and a bull gear, which meshes with the pinion gears. Thereby, it is possible to make the motor relatively low in rotating speed while inhibiting the gears from being increased in diameter, thus enabling achieving reduction in cost.