A constant-current generating circuit, a power-source voltage being applied thereto, generates a constant current. A voltage generating circuit element is connected between the constant-current generating circuit and a fixed voltage point, is supplied with the constant current which is generated by the constant-current generating circuit, and generates a constant voltage. A control circuit detects the current generated by the constant-current generating circuit, and, using the detected current, controls the constant-current generating circuit so that the current to be supplied to the voltage generating circuit element is the constant current.