A power supply degradation determination apparatus which is mounted to the vehicle includes a controller and a DC-DC converter that control execution of a charge phase in which a capacitor capable of accumulating regenerative energy of the vehicle is charged and execution of a discharge phase in which the capacitor is discharged. The controller detects the internal resistance of the capacitor using the difference between the terminal voltage and the open circuit voltage of the capacitor during the execution of the discharge phase and the discharge current thereof, determines whether the internal resistance is a predetermined value or more, and delays the execution start of the discharge phase for a predetermined time when the internal resistance is determined to be the predetermined value or more.