A DC/DC converter capable of preventing abnormal temperature increase in a power transistor. The DC/DC converter comprises a loop circuit, a power transistor, an abnormal high temperature detection circuit, and an abnormality processing circuit. The power transistor supplies an electric current to the loop circuit according to a control pulse signal. The loop circuit accumulates electromagnetic energy in an inductor when the electric current is supplied and generates a negative DC voltage by causing a loop electric current to flow by using the electromagnetic energy accumulated in the inductor when no electric current is supplied. The abnormal high temperature detection circuit detects a normal/abnormal state of temperature of the power transistor. The abnormality processing circuit switches the power transistor off when the abnormal high temperature detection circuit has detected that the temperature of the power transistor is abnormal.