Breakdown of a zapping diode is attained through zapping, and causes a switching transistor to be switched off. The switching transistor is connected in parallel with a current-determining transistor for inducing flow of a constant current and which is diode-connected. When the switching transistor is switched off, a current flows through the current-determining transistor. An adjustment current identical with the current flowing through the current-determining transistor flows through an adjustment current transistor which is connected to the current-determining transistor to form a current mirror. When, on the other hand, no zapping is performed, the switching transistor is switched on and the current-determining transistor is switched off, causing no current to flow through the adjustment current transistor. In this manner, with the current-determining transistor being diode-connected, Vce is a constant value, and the ON-resistance does not affect the magnitude of the adjustment current, enabling attainment of a stable adjustment current.