Stable high frequency high-pressure discharge lamp lighting device avoiding acoustic resonance

A high-pressure discharge lamp lighting device comprising a DC power source, an inverter circuit including at least a pair of switching elements connected to said DC power source for converting a DC signal from said DC power source into an AC signal by turning ON and OFF said switching elements at selectable switching frequencies, a series resonance circuit connected to said inverter circuit and including an inductance element and a capacitor having a resonance frequency f.sub.R, a high-pressure discharge lamp connected in parallel with said capacitor, means for detecting whether said high-pressure discharge lamp is in a lighted state or a non-lighted, non-load state, and control means, coupled to said means for detecting, for changing the switching frequency of said switching elements in response to detection of the lighted state and non-load state of said high-pressure discharge lamp wherein the switching frequency of said inverter circuit in the non-load state of said high-pressure discharge lamp is set by said control means to a frequency f.sub.0 higher than but close to the resonance frequency f.sub.R while said high-pressure discharge lamp is being started into the lighted state with a high voltage generated across said capacitor, and the switching frequency of said inverter circuit is set by said control means to a frequency f.sub.1 lower than the resonance frequency f.sub.R and outside a frequency range in which an unstable arc discharge in said high-pressure discharge lamp due to acoustic resonance occurs while the lighted state of said high-pressure discharge lamp is being maintained with a voltage generated across said capacitor.