DIAGNOSTIC DEVICE AND PROGRAM

A diagnostic device includes: a shutdown command unit that outputs a shutdown command to shut down a power switch with the control of an inverter stopped when a switch diagnostic condition is satisfied in the conduction state of the power switch, an acquisition unit that acquires a voltage change, which is the change in the detected voltage of a voltage sensor in response to the change in the number of revolutions of the motor after the output of the shutdown command by the shutdown command unit, and a diagnostic unit that diagnoses whether the power switch is in an on-failure state based on the voltage change.