A semiconductor device for power supply control includes an on/off control signal generation circuit which generates a control signal for turning on or off a switching element; a current detection terminal to which voltage in proportion to a current flowing in a primary-side winding wire of a transformer is input; a pull-up unit with high impedance provided between the current detection terminal and a terminal to which an internal power supply voltage is applied; and a terminal monitoring circuit which determines that the current detection terminal is abnormal when comparing the voltage of the current detection terminal with a predetermined voltage and detecting that the voltage of the current detection terminal is higher than the predetermined voltage. When the terminal monitoring circuit detects abnormality of the current detection terminal, a signal generation of the on/off control signal generation circuit is stopped by a signal output from the terminal monitoring circuit.