A power circuit abnormality detection method for a power circuit detects whether an abnormality in a power source relay exists. The power circuit includes a pre-charge circuit opening and closing a connection between a direct current power source and a smoothing condenser by bypassing the power source relay to pre-charge the smoothing condenser, and a discharge circuit connected in parallel to the smoothing condenser to discharge electric charges stored in the smoothing condenser via a discharge resistance when a discharge switch is closed. The power circuit abnormality detection method includes a step of detecting whether the open contact abnormality in the power source relay exists based on whether a charge voltage of the smoothing condenser is reduced when a predetermined period of time has elapsed since both the discharge circuit and the power source relay are closed after the pre-charge circuit is opened.