An optical modulation device is disclosed which can suppress production of a cause of degradation such as a void or hillock on a light illumination surface thereof and can be incorporated in an image display apparatus of a small size and a high luminance to improve the reliability of the same. The optical modulation device includes first and second surface elements movable relative to each other to form different diffraction gratings to modulate light inputted thereto. Each of the first and second surface elements has a light illumination surface made of an AlCu alloy material. The optical modulation device has an airtight sealed space in which surrounding gas for the first and second surface elements is encapsulated. The surrounding gas contains hydrogen gas or helium gas or both of hydrogen gas and helium gas.