The present invention provides a boost switching power supply with low switching loss. The boost switching power supply of the present invention includes a coil portion 3a and a first diode 4 that are serially connected between one terminal of a DC power source 2 and one terminal of a first capacitor 5 for smoothing, a first switching element 8 connected between a node A where the coil portion 3a and the first diode 4 are connected and the other terminal of the DC power source 2, a second magnetic element 7 and a second switching element 9 that are serially connected between the node A and the other terminal of the DC power source 2, and a second diode 10 and a second capacitor 11 that are serially connected between a node where the second magnetic element 7 and the second switching element 9 are connected and the node A. According to the present invention, the switching loss of the second switching element 9 is reduced substantially because when the second switching element 9 turns ON, the increase of the current flowing in the second switching element 9 is restricted by the second magnetic element 7 and when the second switching element 9 turns OFF, the increase in voltage across the electrodes of the second switching element is restricted by the charging the second capacitor 11.