A switching power supply IC (21) is provided with, in a form integrated into an integrated circuit: a terminal (T2) whereupon an input voltage (Vin) is applied through an inductor (Lex); a terminal (T3) from which an output voltage (Vout) for a loading LED is extracted; a transistor (N1) connected between the terminal (T2) and a grounding end; a transistor (P1) connected between the terminal (T2) and the terminal (T3); a transistor (P2) connected between the terminal (T3) and a backgate of the transistor (P1); and a switching control section (CTRL) for performing switching control to each transistor. During a step-up operation, the switching control section (CTRL) controls the switching of the transistors (N1, P1) complementarily to each other while continuously keeping the transistor (P2) on, and turns off all of the transistors (N1, P1, P2) when a step-up operation is stopped.