In the present invention a switching control circuit 130 has: a slope voltage generation unit 131 that generates slope voltages Vs1 and Vs2 that are opposite in phase and intersect each other; comparators 132 and 133 that respectively compare the slope voltages Vs1 and Vs2 and a control voltage Vc, and generate comparison signals S1 and S2; and a logical operation unit 134 that generates a step-down control signal D0 and a step-up control signal U0 from the comparison signals S1 and S2. The step-down control signal D0 and the step-up control signal U0 are used to control the switching of a step-up/step-down DC/DC converter.