A discharge lamp lighting device has an oscillation control circuit for determining a frequency with time constant of R and C, a L-C series resonant circuit connected to a half bridge or full bridge operating at the frequency and a circuit in which one end of hot cathodes at both ends of a hot cathode type discharge tube are respectively connected to both ends of a resonant capacitor. A capacitor is further connected in series to other ends of filaments at both ends of the discharge tube for lighting. Dimming of tube current is achieved by changing the oscillation frequency with a DC dimming control voltage by use of a variable capacitor or diode for determining the frequency of the oscillation control circuit. By simultaneously changing the tube current and a filament current of the discharge lamp, the tube current is decreased upon dimming and the filament current is increased.