PURPOSE: To prevent partially or to reduce at least uneven lighting, by making the interval of grating of a grating electrode different in a light source device lighting a fluorescent body.

CONSTITUTION: Grating intervals p,q of the grating electrode 8a corresponding to a damper 11 and of the grating electrode part 8b located at each end region of the light source device are constituted narrower than the grating intervals p', q' in the other grating electrode part 8c. Thus, the electric field between the grating electrode and a filament is stregthened in the grating electrode parts 8a, 8b much more than that in the other grating electrode 8c, and the acceleration in thermoelectrons emitted from the filament is strengthened. As a result, the part deteriorated with lighting is eliminated and the range in the decreased lighting at both ends is reduced.