A vehicular power system includes: a secondary battery; an up-converter receiving a voltage of the secondary battery at a first connection node thereof, and up-converting a voltage between terminals of the secondary battery and outputting the up-converted voltage at a second connection node thereof; system main relays switching between connection and disconnection of the voltage up-converted by the up-converter to and from a load of a vehicle; and a case housing the secondary battery, the up-converter and the system main relays. Preferably the vehicular power supply system further includes a capacitor having one end connected to the second connection node of the up-converter and the case further houses the capacitor. Preferably the capacitor includes a plurality of series connected, electric dual layer capacitors. A vehicular power supply system suitable for being mounted in a vehicle and miniaturized, and a vehicle having the system mounted therein, can thus be provided.