A configuration with which a precharging operation of a capacitive component present on one side of a voltage conversion section can be performed and the current during the precharging operation can be controlled is realized more simply. An on-board power supply device includes a charge circuit section which is connected in parallel with a voltage conversion section between a first conduction path and a second conduction path, and which performs a step-down operation in which a voltage applied to the second conduction path is stepped down by a switch portion switching on and off and an output voltage is applied to the first conduction path. A control unit outputs a second control signal that alternately switches between an on signal and an off signal to the switch portion of the charge circuit section when a predetermined precharging condition is satisfied.