To shorten the time for filling a tank with gas by increasing delivery quantity of gas when suction pressure drops.

An air compressor 11 is provided with a compression part 14 driven by an electric motor 12, and a control circuit 26 controlling drive of the electric motor 12. A suction pressure sensor 24 is connected to a suction port 19 of a compression part 14 via a pressure pipe 25. Rotation speed of the electric motor 12 is increased according to suction pressure Pin when suction pressure Pin detected by the suction pressure sensor 24 gets lower than a reference pressure range P0.