According to one embodiment, a transmitter includes a housing, an internal member, a first unit, and a second unit. The internal member is fixed to the housing. The internal member forms a first area and a second area inside the housing. The first area communicates with an outside of the housing. The second area is liquid-tightly partitioned from the first area. The first unit is in the housing. The first unit includes a first heat sink and a first circuit. The first heat sink is at least partially in the first area. The first circuit is in the second area. The second unit is in the housing. The second unit includes a second heat sink and a second circuit. The second heat sink is at least partially in the first area and facing the first heat sink. The second circuit is in the second area.