Abstract: In a driving circuit which is used together with a flash lamp supplied with an exciting voltage and which comprises a transformer responsive to a trigger pulse for developing a pulse voltage and an exciting member around the lamp for causing a discharge to occur in the lamp in response to the pulse voltage to energize a laser device placed adjacent the lamp, a control member disposed between the transformer and the exciting member allows the pulse voltage to be applied across the lamp and suppresses a parasitic voltage which is otherwise developed across the transformer as a result of the discharge. The control member may comprise an air gap that is preferably from one to several millimeters long.