PURPOSE: To obtain the accurate reference electric quantity that is not easily affected by a change of capacitance, by charging a capacitor with the reference voltage just for a period of the pulse width of a charging pulse and then discharging the capacitor with a discharging pulse.

CONSTITUTION: When a timing control circuit 12 is triggered by a synchronizing pulse 11, a charging pulse 19 is delivered from the circuit 12 and fed to an FET switch 13. Thus a switch 13 is changed over, and the reference voltage 15 is applied to a capacitor 17 via the switch 13 and a resistance 16 to charge the capacitor 17. A discharging pulse is generated from the circuit 12 after the generation of the pulse 19 and fed to an FET switch 14. As a result, the switch 14 is changed over. Then the electric quantity stored at the capacitor 17 is delivered through a resistance 18 to obtain the reference electric quantity. Thus the resistance 18 affects only the discharging time and does not affect directly the accuracy and the level of the electric quantity.