Optical module having restriction body fixed to stem and having a linear thermal expansion coefficient smaller than that of the stem

An optical module includes: a stem including a first surface and a second surface opposite to the first surface; a thermoelectric cooler including a heat-releasing substrate fixed to the first surface; a semiconductor laser element attached to the thermoelectric cooler; a cap fixed to the first surface and covering the thermoelectric cooler and the semiconductor laser element; a lens fixed to the cap; and a restriction body fixed to the second surface. The linear thermal expansion coefficients of the heat-releasing substrate and the restriction body are smaller than the linear thermal expansion coefficient of the stem.