PURPOSE: To provide the radio transmitter which can economically and easily added.

CONSTITUTION: The size of a high frequency switching unit 4 is made same as the size of a transmission filter unit 2A. Namely, the high frequency switching unit 4 and the transmission filter unit 2A are formed in the same shape. The transmission filter unit 2A is detached and at that position, the high frequency switching unit 4 is mounted. Therefore, when adding active and spare radio transmitters after initially installing the radio transmitter, the units can be effectively utilized and the same frame to be added is available as well. Further, it is not necessary to prepare any other enclosure for the high frequency switching unit to be added.