PURPOSE: To attain miniaturization with the process of fabrication simplified, by mutually connecting nonlinear elements via through holes so as to constitute a ring modulator.

CONSTITUTION: On both top and reverse sides of dielectric substrate 21, thin conductor plates 22a∼22d forming strip lines are provided. At intermediate cut part 23, ring modulator 28 consisting of chip-shaped diodes 24∼27 is formed. Diodes 24 and 25 are provided on cut parts 29 and 30 of plates 22a and 22c and diodes 26 and 27 are fitted on lands 31 and 32 insulated from plates 22a and 22b. Near intermediate cut part 23, through holes 33∼36 penetrating dielectric substrate 21 are further provided and through them, four chip-shaped diodes 24∼27, nonlinear elements, are mutually connected so as to constitute the ring modulator.