To provide a parallel drive power supply having a simple constitution and enabling a high-accuracy current balance control.

Input currents to DC/DC converters 1A, 1B flow into windings 21A, 21B of a current transformer 21. Magnetic fields are generated by the input currents in the direction for making the magnetic fields cancel each other. Output from the DC/DC converters 1A, 1B are controlled so as to make the magnetic fields cancel each other. The windings 21A, 21B for flowing the input currents into the DC/DC converters 1A, 1B are wound onto the magnetic core 21C of the current transformer 21 in reverse polarity. A winding 21D for flowing an excitation current ip from an oscillator 22 is wound onto the magnetic core 21C. The imbalance of positive and negative peaks of the excitation current ip is generated from the nonlinear characteristic of the BH curve of the magnetic core 21C, and detected by a detector 23. A control unit 24 controls the DC/DC converters 1A, 1B so as to eliminate the imbalance.