A submount includes a substrate, the substrate including: a first surface; a second surface that is perpendicular to the first surface; a third surface that is perpendicular to the first surface and the second surface; a fourth surface that is perpendicular to the first surface and the second surface, and is opposed to the third surface; a fifth surface that is perpendicular to the second surface and the third surface, and is opposed to the first surface; a sixth surface that is opposed to the second surface; a first notch part that is provided in a portion at which the second surface and the third surface are adjacent to each other; and a second notch part that is provided in a portion at which the second surface and the fourth surface are adjacent to each other, the first notch part and the second notch part each having a recessed surface.