A current limiting circuit for a boost converter includes a voltage divider circuit between a main switch which flows a current to an inductor and a comparator included in a current detecting circuit. The voltage divider circuit includes two transistors of the same type as that of the main switch, which are connected in series. One of the two transistors is a sub-switch which is connected between a voltage division point and a drain terminal of the main switch, and is turned on/off in synchronization with the main switch in accordance with an output signal of a control circuit. The other transistor is a detection resistance transistor which is connected between the voltage division point and a source terminal of the main switch, and whose gate terminal is connected to a bias voltage so that the detection resistance transistor is always on.