An optical transmitter according to one embodiment includes a housing with an emission end, a light emitting element mounted on a first mounting portion of the housing, and a light receiving element mounted on a second mounting portion of the housing to monitor output light from the light emitting element. The second mounting portion is provided with a carrier, a first resin located on an emission end side of a lower side of the carrier, and a second resin located on a light emitting element side of the lower side of the carrier. A coefficient of thermal expansion of the first resin is smaller than a coefficient of thermal expansion of the second resin.