An optical module includes a mounting board, an optical element, an optical fiber having an optical axis, the optical fiber inserted in the mounting board to align the optical axis with the optical element, and a positioning mark provided to position the optical element on the mounting board. The mounting board has a groove provided in the middle of the mounting board and extending in a direction of the optical axis of the optical fiber, the groove enclosing the optical fiber when inserted. The groove has a vertical wall which is perpendicular to the direction of the optical axis and confronts a leading edge of the optical fiber when inserted. The positioning mark is located adjacent to an internal edge of the groove where the vertical wall is provided on the mounting board.