A piezoelectric transformer comprising a rectangular piezoelectric body (23) divided into first to fourth regions (A1 to A4) in the longitudinal direction, planar electrodes (24, 25, 26, and 27) provided in the first and fourth regions (A1 and A4) as input electrodes, and belt-like electrodes (30 and 31) provided at the boundary between the other two regions (A2 and A3) as output electrodes and polarized oppositely in the longitudinal direction. By applying an AC input voltage of the frequency corresponding to the wavelength equal to the length of the piezoelectric body (23) to the input electrodes, the piezoelectric body (23) is vibrated in a one-wavelength resonance mode and the voltage generated by the piezoelectric effect resulting from the vibration is taken out of the output electrodes. This transformer has a small size, generates little vibration speed heat, and is efficient. In a modification of the transformer, the input electrodes can be installed, not in the first and fourth regions, but in the other two regions in which the displacement distributions are symmetrical or opposite in the one-wavelength resonance mode, and the output electrodes are installed in the other regions. In another modification, the first and second areas serve as the input section and are formed separately from the output section of the third and fourth regions and the input and output sections are stuck to each other.