To provide a charging/discharging circuit of a small scale by using a differential circuit which performs charging/discharging operations by means of charging/discharging current received from a current source and based on a control signal.

When a control signal has a high level, a PNP transistor TR Q21 and an PNP TR Q22 are turned on and off respectively. Thus, no current flows between the emitter and connector or the TR Q22, and a charging/ discharging current Is flows between the emitter and collector of the TR Q21. As a result, a current mirror circuit 30 operates. That is, the current Is flows between the collector and emitter of an NPN TR Q32 when the current Is flows between the collector and emitter of an NPN TR Q31. Thus, a discharging current is sucked through an output terminal OUT. As a charging/discharging circuit consists of a current source 10, a differential circuit 20 and the circuit 30, the scale of the charging/discharging circuit is reduced and this circuit is easily designed.