PURPOSE: To easily vary and set the pulse width of a trigger output pulse with a high precision by inverting a flip flop again at the time when the flip flop is set to the inverted state by the external trigger input and a capacitor is charged to reach a certain voltage.

CONSTITUTION: When a flip flop 6 is set to the inverted state by the external trigger input, a capacitor 4 set to the discharging state by a second semiconductor switch 3 till then is set to the charging state. The capacitor 4 is charged like a ramp by the current from a programmable constant current source passing a first semiconductor switch 2; and when it is detected by a comparator 5 that the charging voltage reaches the certain voltage, the flip flop 6 is inverted again by the detection output, and the charged electric charge of the capacitor 4 is discharged through the second semiconductor switch 3 to prepare for the external trigger input. Thus, the trigger output pulse width is easily varied and set with a high precision.