PURPOSE: To stably keep an output level, by correcting a switching duty so that the estimated variable component of source voltage may be compensated in synchronism with the predetermined ON/OFF-timing of a load.

CONSTITUTION: With the power source device of a duplicator or the like, a DC-DC converter circuit is organized and is set system by system. Its control circuit is provided with a microcomputer IC1 and an integrated circuit IC2, and for example three output units 251∼253 are controlled in drive via repective drivers 241∼243 on a primary side. The output units 251∼253 are composed of a transformer, a rectifier, and the like, and current is fed to a main charger, a transfer charger, and the like. In this case, in order to suppress output fluctuation due to the disturbance of a power source circuit, processing by the microcomputer IC1 is controlled so that it may be compensated synchronized with the ON/OFF-timing of the other load, for example, the main charger or the like. Then, the delay of a compensating action with the microcomputer IC1 can be avoided.