PURPOSE: To obtain an optical node element which puts all of light signals into a through state and is not instantaneously interrupted at the time of tuning by providing one optical waveguide with a means for periodically implanting currents or impressing electric fields.

CONSTITUTION: This optical node element has two pieces of the optical waveguides 2, 4 which are not equal in propagation constant on the semiconductor substrate 1. Both exist in parallel and proximity with and to each other to the extent that a part of the field of the light propagating in a part thereof bleeds to the other waveguide. At least one of the optical waveguides is provided with the means for periodically implanting the currents or impressing electric fields. The refractive index of the second waveguide 4 of the element receives periodic perturbation by the current implantation and a perfect coupling is obtd. between the two waveguides at a certain wavelength. The perfect coupling is determined by the period of the current implantation. All the light beams attain the through state when the currents are not implanted. The element is made into the through state for the light signals of all the wavelengths in the off state in such a manner and is operated without instantaneously interrupting the other channels transmitted thereto at the time of changing the off state to the on state.