The invention provides a vehicle power supply system that, even when a high-voltage electricity storage device fails and is interrupted, makes it possible for a power generator to generate power without complicating the system and increasing cost. The vehicle power supply system is characterized as follows: while a current interrupting mechanism is interrupting the charging and discharging of a second electricity storage device, a DC/DC converter is controlled to a state in which power is supplied from the low-voltage side to the high-voltage side, converts the input voltage on the low-voltage side so that the output voltage on the high-voltage side becomes a predetermined voltage, and supplies power to a field winding on the basis of the predetermined voltage to raise the voltage induced in the armature winding of an AC power generator. After the induced voltage of the AC power generator has reached a predetermined state in which power can be supplied to the low-voltage side, the control of the DC/DC converter is changed from the state in which power is supplied from the low-voltage side to the high-voltage side to a state in which power is supplied from the high-voltage side to the low-voltage side, and the power generated based on the induced voltage of the AC power generator is supplied to the low-voltage side.