A transmission apparatus includes a case including first, second, and third stages, each stage having one slot, each slot allowing free insertion and removal of a board; a first control board; a first communication unit connected with the first control board and performing radio communication; and a second communication unit connected with the first control board and performing communication faster than the radio communication. The first control board is mounted in the slot of the first stage. The first communication unit is mounted in the slot of the second stage, and the second stage is provided on one side of the first stage. The second communication unit is mounted in the slot of the third stage, and the third stage is provided on a side opposite to the first communication unit with respect to the first stage. The second communication unit is arranged adjacent to the first control board.