To provide a step-up/step-down converter where a circuit structure is simplified, without generating the switching control signal of a step-up switching element.

A step-down switching element is switch-controlled by the switching control signal. In a step-down mode, the step-up switching element is off-operated. In a step-up mode, the step-up switching element is switch-controlled, in synchronization with the step-down switching element with a switch output signal appearing in the output end, as the switching control signal of the step-up switching element by the switching operation of the step-down switching element.