A DC-DC converter of a synchronous rectification type includes a synchronous rectification transistor and a backflow detection circuit which detects a reverse current based on a voltage across the synchronous rectification transistor. The backflow detection circuit includes a first-stage differential input circuit including a first transistor, a first resistor, a second transistor, a second resistor and a fifth transistor, and a second-stage differential input circuit including a third transistor and a fourth transistor. The fifth transistor is of a same conductive type as the synchronous rectification transistor and contains a drain connected to the other end of the first resistor with respect to an end connected to the first transistor.