An optical module that is easy to manufacture and may arrange and position an optical element mounting substrate and a package with high precision is provided. A substrate side positioning groove portion is formed in an optical element mounting surface of the optical element mounting substrate on which an optical element is mounted, and a package side positioning groove portion is formed in the package on which the optical element mounting substrate is arranged. The optical element mounting substrate and the package are overlapped with each other with the substrate side positioning groove portion and the package side positioning groove portion facing each other. An optical fiber that is a positioning member is inserted between the positioning groove portions. Thus, the optical element mounting substrate and the package are positioned relative to each other. The respective positioning groove portions on the substrate side and on the package side may readily be formed with high precision. Also, the optical fiber may be manufactured with high precision. Thus, it is possible to position the optical element mounting substrate and the package with very high precision.