A transmission apparatus which is capable of maintaining excellent EMC performances even if the number of cables to be connected thereto is increased. An electronic circuit unit is plugged into a subrack from the front of the subrack. A connector unit-receiving block is arranged on the rear surface of the subrack. A connector unit connectable with an external cable to be connected to the electronic circuit unit is plugged into the rear of the subrack at the rear of the electronic circuit unit, for being received within the connector unit-receiving block. The connector unit is configured such that a metal shield case covers a connector board having a connector mounted thereon.