To provide a control circuit and control method of a step-up/step-down type DC-DC converter capable of realizing high efficiency. In a state (1), a terminal Tx of a choke coil L1 is connected to an input terminal Tin, and a terminal Ty is connected to a reference potential. In a state (2), the terminal Tx is connected to the reference potential, and the terminal Ty is connected to an output terminal Tout. In the state (3), the terminal Tx is connected to the input terminal Tin, and the terminal Ty is connected to the output terminal Tout. A first period operation TO1 is constituted by the states (1) and (2), and a second period operation TO2 is constituted by the states (1) and (3). A second period T2, in which the second period operation TO2 is performed, is a value n times as long as a first period T1, in which the first period operation TO1 is performed. In the second period operation TO2, the state (1) is switched to the state (3) so that an increasing slope of an inductor current IL is reduced.