Disclosed is an on-board charging system in which, when a plurality of charging circuits is connected in parallel between input and output terminals, operation timings of switching circuits in the respective charging circuits are interlocked to minimize ripples of an input alternating current. The on-board charging system includes: a plurality of charging circuits configured to each have a power factor correction circuit portion for correcting a power factor of alternating current input power by pulse width modulation control of a switching element and to be connected in parallel with each other between an input terminal of the AC input power and an output terminal connected to an object to be charged; and a controller configured to interlock the switching elements to generate a PWM control signal for performing PWM control.