To provide a voltage resonance power supply device which can be embodied in a small construction and at a low cost and which is equipped with enhanced reliability.

When an On signal for a fluorescent lamp is fed to a control circuit 4, a current transformer 63 of a resonant condition sensing circuit 62 senses the current flowing in a transistor 60 and converts it into a voltage, and the obtained voltage is fed to a zenor diode 65. When the voltage remains as not attaining the zenor voltage, a transistor 66 is turned off, and an On-Off control part 45 puts off the fifth PWM signal. If thereafter the voltage value exceeds the zenor voltage, the transistor 66 is turned on, and the fifth PWM signal is put On. This operating cycle is repeated until the fluorescent lamp 47 lights up.