To provide an air compressor that can exercise high discharging performance by driving a direct current brushless motor 2 at a high revolution speed for work requiring large consumption of compressed air, and that can lower operation noises by operating the motor 2 at a low revolution speed for work requiring small air consumption.

In an air compressor 1 where compressors 3 and 4 are driven by a direct current brushless motor 2 to compress air and store it in an air tank 6, there is provided an inverter circuit 9 for rotating and driving the motor 2 based on a revolution command signal 11 output from a control circuit 10, and the air compressor 1 detects increase/decrease of the amount of compressed air in the tank 6 and makes the control circuit 10 output the signal 11 to the inverter circuit 9 to decrease or increase the revolutions based on the detection result.