To solve the following problem; as to a lighting device used for a liquid crystal backlight, which uses a piezo-electric inverter having a piezo-electric transformer as a voltage boosting means, and mainly drives a large-sized cold cathode discharge tube, since conventional piezo-electric inverters are mostly ones with applied power of about 3 W, and if more than 5 W is applied, generation of high heat and thermal runaway are caused and the piezo-electric inverter is eventually broken, the limit of output wattage has not been exceeded.

An oscillation mode in a twisting direction generated during high power drive, and an oscillation mode in a meandering direction are completely prevented from being generated by making a rigid part comprising a non-polarized part in the center part of this piezo-electric transformer. Thereby, this highly efficient, light, and thin high power piezo-electric transformer wherein rise of its temperature is saturated at low temperatures can be obtained.