PURPOSE: To provide a process for production which entirely eliminates the need for a stage for patterning periodic electrodes on a waveguide substrate and a stage for etching these periodic electrodes and is capable of providing excellent SHG elements of a pseudo phase matching type with good accuracy.

CONSTITUTION: An electrode plate 4 formed with the comb-shaped periodic electrodes 5 on its one main surface is placed on a substrate 1 consisting of a nonlinear optical material formed with waveguides 6 on its one main surface and a rear surface electrode 3 on its other main surface in such manner that the periodic electrode 5 face the waveguides 6. Polarization inversion regions periodically inverted with spontaneous polarization are formed in the waveguides 6 by applying voltage between the periodic electrodes 5 and the rear surface electrode 3.