To provide a vehicular power supply system capable of suppressing consumption of electric power charged into a high-voltage battery, and performing charging without burdening an auxiliary equipment battery for long service life of the auxiliary equipment battery.

The vehicular power supply system comprises: a motor that drives wheels; a high-voltage battery that supplies electric power to the motor; an auxiliary equipment battery that supplies electric power to auxiliary equipment; a DC-DC converter that steps down a voltage of the high-voltage battery and charges the auxiliary equipment battery by the voltage stepped down by the DC-DC converter, and further includes voltage control means that changes an output voltage of the DC-DC converter according to power consumption of the auxiliary equipment.