A converter includes a converter circuit including a rectifying section to rectify an alternating current (AC) voltage and a smoothing section to smooth a direct current (DC) voltage rectified by the rectifying section, a diagnostic device configured to diagnose an abnormality of the converter circuit, an inrush current preventing section configured to prevent inrush current from being supplied to the smoothing section, and a switching section configured to supply the AC voltage to the converter circuit through a path different from a voltage supply path of the inrush current preventing section, wherein the diagnostic device determines an abnormal region of the converter circuit by controlling the inrush current preventing section and the switching section.