PURPOSE: A manufacturing method of an optical modulation device is provided to form a uniform interface by preventing etching of an upper insulating layer after protecting the upper insulating layer with a mask layer when the protective layer is wet-etched. CONSTITUTION: A manufacturing method of an optical modulation device includes the following steps: forming an insulating layer(120) on a substrate(110); forming a sacrificial layer(130) on the insulating layer; forming a structural layer(140) on the sacrificial layer; forming a protective layer(150) on the structural layer; forming a piezoelectric driving body on the both ends of the structural layer; laminating the upper insulating layer on the structural layer; etching the upper insulating layer with a first mask layer; forming a second mask layer; and etching the protective layer after patterning the second mask layer.
