the invention realizes an optical modulator which prevents occurrence of an edge breakdown and is improved in extinction characteristic and voltage resisting property . the optical modulator comprises an oxide film formed as a growth inhibiting film on a compound semiconductor substrate of a first conduction type , a double heterostructure including a clad layer of the first conduction type , a light absorbing layer and a clad layer of a second conduction type successively formed in an opening of the oxide film , and an embedding structure for covering over the entire double heterostructure . the optical modulator is characterized in that the carrier concentration of the clad layer of the first conduction type exhibits a continuous variation from the semiconductor substrate to the light absorbing layer or the carrier concentration of the embedding structure portion exhibits a variation from a low concentration to a high concentration .