An optical module in which an optical element is housed in a housing includes: an optical window member through which input light to the optical element or output light from the optical element passes and which hermetically seals inside of the housing; and a holding member that holds the optical window member. The optical window member is fixed to the housing by the holding member. A difference between linear expansion coefficients of the holding member and the optical window member is smaller than a difference between linear expansion coefficients of the housing and the optical window member. A position where the optical window member is attached on the holding member protrudes to an optical element side from a position where the holding member itself is fixed.