To reduce the noise of a constant current circuit.

A semiconductor substrate is formed by incorporating a reference voltage generating circuit 11, an arithmetic amplifier AMP1 for amplifying a generated reference voltage, a transistor M1 for receiving the output voltage, a resistance ladder 17 serially connected to this transistor, a switch circuit 14 for selectively feeding back the taps of the ladder 17 to the input terminal of the arithmetic amplifier, a trimming circuit 19 for controlling the operation of this switch circuit and a monitor pad 15, enabling external monitoring of a current flowing through the resistance ladder, thereby the ground level of the resistance ladder is equalized with the ground level of another circuit formed at the semiconductor substrate to attain noise reduction.