An optical modulator includes an optical modulation element including an optical waveguide formed on a substrate and a housing that accommodates the optical modulation element, the housing has a bottom surface wall having a quadrilateral shape in a plan view, first and second long side walls that are connected to two opposite edges of the bottom surface wall, and first and second short side walls that are shorter than the first and second long side walls and are connected to two other opposite edges of the bottom surface wall. An average wall thickness of the second long side wall is equal to or larger than an average wall thickness of the first long side wall. At least one of the first and second short side walls has an average thickness that is thinner than the average thickness of the first long side wall.