An object of the present invention is to provide a computer power supply in which, by improving the circuit itself, internal heat loss can be reduced, thereby greatly improving efficiency. A partial resonance circuit 8 is constituted by a primary side winding N1 of a high frequency transformer 3, a resonance condenser 7, and two switching elements Q1, Q2, a secondary side output circuit 4 for driving a load is connected to a secondary side of the high frequency transformer 3 via a winding, and a reverse converter 11 for driving and halting the first switching element and second switching element by causing the respective phases thereof to differ on the basis of a driving signal is provided.