The invention downsizes and simplifies structures of a compressor and its
driving system apparatus, and achieves a reduction of a noise. An oil
free screw compressor is constituted by compressor main bodies
compressing a gas, a motor driving rotors of the compressor main bodies
via step-up gears, a gear casing storing the step-up gears, cooling
apparatuses cooling a discharge air and the like. An oil tank is provided
independently from the gear casing, the motor is fixed to a common base,
the gear casing is integrally attached to the motor via a flange, and the
compressor main bodies are integrally attached to the gear casing via the
flange. Further, the cooling apparatuses are arranged in an upper side of
the driving system apparatus, and a cooling fan is installed in an upper
side thereof.