PURPOSE: To generate a pseudo sine wave having less higher harmonic components from a rectangular wave pulse signal, by using a charging and discharging circuit for a capacitor and a delay circuit in combination.

CONSTITUTION: When a rectangular wave pulse signal which rises at time t1 is inputted to a terminal 1, a capacitor C is charged with a constant current (in period A). The rectangular wave pulse signal is supplied to a delay circuit 3 to generate a signal (b) and a switching circuit 4 which receives the signal (b) generates outputs Q1 and Q2. The output Q1 closes a switch S1 and consequently, the capacitor C is charged abruptly (in period B1) and is saturated (in period B2). When the rectangular pulse signal falls at time t2, the capacitor C discharges the constant current (in period A'). Further, the output Q2 closes a switch S2, and the capacitor C is discharged abruptly (in period B'1) to a certain voltage (in period B'2). Thus, a pseudo sine wave having less higher harmonic components is generated.