To stably support a piezoelectric transformer element by including a foamed plastic as a means for fixing the piezoelectric transformer in the single-layer-type or lamination-type piezoelectric transformer.

A single-layer Rosen piezoelectric transformer element 1 in semi-wavelength mode is fixed to a circuit substrate 5 by foamed plastic 4. An input electrode 2 is formed at the upper and lower parts of one side in the single-layer Rosen piezoelectric transformer element 1 in semi-wavelength mode. A lead wire 6 is connected to the input electrode 2, an output electrode 3 is formed at the other edge part, and the lead wire 6 is connected to the output electrode. Foamed plastic to be used is made of, for example, relatively hard PU foam. The hard PU foam can be formed in many ways and a spray type with one-pack type which is hardened by moisture in air can also be used.