PURPOSE: To provide an IC with built-in constant current circuit which reduces the area occupied by the constant current circuit.

CONSTITUTION: This IC incorporates the constant current circuit composed of a current mirror circuit 1 for deciding a current ratio and a transistor circuit 20 for deciding a current value, and the transistor circuit 20 is provided with the pair of current-mirror-connected transistors Q3, and Q4, resistor 21 with a prescribed temperature coefficient so as to let an emitter current I1 of the transistor Q3 with a narrower emitter in the transistor pair flow and resistor 22 with a prescribed temperature coefficient to let an emitter current 12 of the transistor with the wider emitter flow, and the value of the resistor 22 is larger than that of the resistor 21.