To prevent double pulses from being formed without inducing ringing or overshoot when a pulse is generated by a method wherein a resistor and a switching device are connected to the electrodes of an electro-optical device, and the switching device is turned on/off to feed a rectangular voltage to an electro-optical device.

High-voltage power supplies 21 and 22 are provided for trapping and cavity damping. Resistors 23 and 24 are connected to the electrodes 10a and 10b of a Pockels cell 10 respectively, the resistor 23 is connected to the positive electrode of the high-voltage power supply 21, and the resistor 24 is grounded. Switching devices 25 and 26 are connected to the electrodes 10a and 10b. The switching device 25 is connected to the positive electrode of the high-voltage power supply 22 and directly connected to a resistor 24 which is grounded, and the switching device 26 is grounded and directly connected to the resistor 23 connected to the high-voltage power supply 21. A control circuit 27 turns the switching devices 25 and 26 on or off to apply a rectangular voltage between the electrodes 10a and 10b.