A DC-DC converter includes an Nch FET.sub.1 which is series connected between an input terminal and an output terminal, and an Nch FET.sub.2 which is connected between the output terminal side of the Nch FET.sub.1 and a ground terminal. On the output terminal side of the circuits, a smoothing circuit and a comparator circuit are connected. The output side of the comparator circuit is connected to an on-time limiter circuit, and the on-time limiter circuit is connected to an H/S driver circuit for controlling the Nch FET.sub.1 through an inverter and directly connected to an L/S driver circuit for controlling the Nch FET.sub.2. Here, when a switching control signal for turning on the Nch FET.sub.1 is input to the on-time limiter circuit from the comparator, the on-time limiter circuit detects a time in the on state and outputs a signal by which the Nch FET.sub.1 is temporarily off controlled.