A vehicular power supply system, comprising: a plurality of system-based paths branched from a power supply path of a vehicle; a main power distribution box comprising a plurality of main semiconductor switching devices, each of the plurality of main semiconductor switching devices provided in a part of a corresponding system-based path; a plurality of load-based paths branched from each of the system-based paths; and a plurality of sub power distribution boxes each provided in a corresponding system-based path, each of the plurality of sub power distribution boxes comprising a plurality of sub semiconductor switching devices provided in a part of a corresponding load-based path, characterized in that the main power distribution box further comprises a main controller for performing control to switch between conduction and non-conduction states of each of the plurality of main semiconductor switching devices; each of the sub power distribution boxes further comprises a sub controller for performing control to switch between conduction and non-conduction states of each of the plurality of sub semiconductor switching devices and for transmitting passage current values of the plurality of sub semiconductor switching devices to the main controller the main controller is configured to determine an overcurrent state of each of the plurality of sub semiconductor switching devices based on the passage current values of the plurality of sub semiconductor switching devices transmitted from the sub controller, the main controller is configured to notify a corresponding sub controller that one sub semiconductor switching device of the plurality of sub semiconductor switching devices is in the overcurrent state, when it is determined by the main controller that the one sub semiconductor switching device is in the overcurrent state, and the corresponding sub controller is configured to execute interruption processing for switching the one sub semiconductor switching device notified of the overcurrent state from the conduction state to the non-conduction state. a plurality of system-based paths branched from a power supply path of a vehicle; a main power distribution box comprising a plurality of main semiconductor switching devices, each of the plurality of main semiconductor switching devices provided in a part of a corresponding system-based path; a plurality of load-based paths branched from each of the system-based paths; and a plurality of sub power distribution boxes each provided in a corresponding system-based path, each of the plurality of sub power distribution boxes comprising a plurality of sub semiconductor switching devices provided in a part of a corresponding load-based path, characterized in that the main power distribution box further comprises a main controller for performing control to switch between conduction and non-conduction states of each of the plurality of main semiconductor switching devices; each of the sub power distribution boxes further comprises a sub controller for performing control to switch between conduction and non-conduction states of each of the plurality of sub semiconductor switching devices and for transmitting passage current values of the plurality of sub semiconductor switching devices to the main controller the main controller is configured to determine an overcurrent state of each of the plurality of sub semiconductor switching devices based on the passage current values of the plurality of sub semiconductor switching devices transmitted from the sub controller, the main controller is configured to notify a corresponding sub controller that one sub semiconductor switching device of the plurality of sub semiconductor switching devices is in the overcurrent state, when it is determined by the main controller that the one sub semiconductor switching device is in the overcurrent state, and the corresponding sub controller is configured to execute interruption processing for switching the one sub semiconductor switching device notified of the overcurrent state from the conduction state to the non-conduction state.