PURPOSE: To enable the pressure of the gas charged in a fluorescent lamp to be easily measured without breaking the lamp by comparing a tube voltage waveform obtained when the lamp is ignited with the relationship between the pressure of the charged gas and the waveform.

CONSTITUTION: A fluorescent lamp 1 is ignited with a resonance-type stabilizer 2 having a secondary no-load voltage waveform consisting of multiple resonance waves. An osiclloscope 3 is used to determine the amplitude (A) of the depressed point 10 of restrike voltage 9 in a tube voltage waveform 8 as well as the time (T) between the rising point and the depressed point 10 of the restrike voltage 9 in the tube voltage waveform 8. Accordingly, by obtaining beforehand the relationship between the pressure of the charged gas and the A value or T value of a tube voltage waveform for each type of a fluorescent lamp, the pressure of the gas charged in a fluorescent lamp can be easily obtained without breaking the lamp.