An optical measurement apparatus includes a hemispherical portion having a diffuse reflection layer on an inner wall, and a plane portion disposed to involve a substantial center of curvature of the hemispherical portion and close an opening of the hemispherical portion, and having a reflection layer on an inner surface side of the hemispherical portion. The plane portion includes: at least one of a window for introducing light to be homogenized in an integrating space formed between the hemispherical portion and the plane portion, and a window for extracting light homogenized in the integrating space; an outer portion formed of a first material chiefly causing specular reflection, and occupying at least a region of a predetermined width from an outermost circumference; and an inner portion formed of a second material chiefly causing diffuse reflection and having a higher reflectance for at least an ultraviolet region than the first material.