PURPOSE: To provide the manufacture of the waveguide type optical device having signal electrodes which are small in the loss of a propagated microwave signal in the manufacture of a waveguide type optical device such as an optical modulator and an optical switch utilizing electrooptic effect.

CONSTITUTION: After a substrate electrode 16 and the signal electrodes 14 confirming with a resist pattern 17 is formed on a substrate 11 provided with an optical waveguide 12, the top surfaces of the signal electrodes are flattened by etching. Then the resist pattern 17 and the substrate electrode 16 are removed to obtain the waveguide type optical device. The signal electrodes 14 having small raggedness on the top surfaces are obtained by this manufacture, so the microwave loss of the signal electrodes is reduced to widen the band of the wavegude type optical device and makes the operation fast.