Air compressor and method of controlling annunciation

To announce whether primary voltage values are voltage values suitable for driving a motor means or not to a worker by detecting primary voltages supplied from a drive source. This air compressor comprises a compressed air generating means for generating compressed air, a tank part for reserving the compressed air generated by the compressed air generating means, the motor means for driving the compressed air generating means, control means 5, 20 for controlling the driving quantity of the motor means, a voltage detection means 28 for detecting the primary voltages supplied by the drive source for driving the motor means, and annunciation means 6, 7 for annunciation. The control means 5, 20 classify the primary voltage values detected by the voltage detection means 28 with reference to a predetermined set voltage value required for driving the motor means. The annunciation means 6, 7 change the annunciation method according to the primary voltage values classified by the control means 5, 20.