Switching power supply circuit and switching power supply device

The present invention addresses the problem of suppressing excessive heat generation in a circuit for a switching power supply. A power supply IC (10) for a switching power supply device, which generates an output voltage (Vout) on the basis of an input voltage (Vin), is provided with: a high-side transistor disposed between an input terminal (IN) to which the input voltage is applied and a switching terminal (SW); and a low-side transistor disposed between the switching terminal and a ground terminal (GND). Feedback control for turning the transistors on or off is performed on the basis of a feedback voltage corresponding to the output voltage. The protection circuit (140) is capable of performing a protection operation for turning on the high-side transistor or the low-side transistor without depending on feedback control on the basis of a switching voltage at the switching terminal and an input voltage, on the basis of a reverse current flowing from the ground terminal to the switching terminal, or on the