An air conditioner includes an inverter circuit, a control unit that controls the inverter circuit, a compressor having a protection device (a pressure switch), and a phase-voltage detection circuit (a U-phase voltage detection circuit) that detects a voltage at any of three-phase windings (compressor windings) of the compressor. The control unit includes a shutdown-cause specifying unit that determines presence or absence of an operation of the protection device based on a phase voltage value detected by the phase-voltage detection circuit, by turning on any of a plurality of switching elements constituting the inverter circuit, after the compressor has been shut down, and specifies a cause of the shutdown of the compressor.