An optical module includes a first optical block and a second optical block. The first optical block includes a base part, two extending parts which extend in a first direction, locking parts, and a first reference surface. The second optical block includes a holding part, two arm parts, spring pieces which extend in the first direction, locked parts which are formed on the spring pieces, and a second reference surface. In a state that the first optical block and the second optical block are assembled with each other, the locking parts are hooked on the locked parts, the second reference surface is pressed against the first reference surface by a spring force of the spring pieces so as to realize positioning in the assembling direction, and an optical path between the base part and the holding part is parallel to the first direction.