PURPOSE: To enhance the responsiveness in simple constitution by moving the discharge column due to a pair of discharge electrodes, which are arranged so that the spacing widens by and by, through the action of magnetic field.

CONSTITUTION: Discharge start voltage is impressed, and needle-shaped start electrodes 4, 4' of a head light 1 starts discharging. When discharge due to discharge electrodes 3, 3', whose spacing widens backward from, is stabilized by a discharge maintaining voltage generating device, discharge by the mentioned electrodes 4, 4' stops. When magnetic field is impressed perpendicularly to a discharge column 13 formed in the narrowest part of the spacing of electrodes 4, 4' through a coil 6, electric charges moving the discharge column 13 displace according to the strength of the magnetic field, and the light pattern of irradiating light varies with good responsiveness. Thereby the responsiveness can be enhanced in simple constitution.