A relay apparatus includes: ports for transmitting and receiving communication data; a relay process portion that executes a relay process of transmitting the communication data received from at least one of the ports, from a destination port corresponding to the at least one of the ports connected to a destination device in accordance with a destination for the communication data; and a setting portion that, by an instruction from at least one external device, sets each of the ports to either a relay prohibition state in which relay of the communication data is prohibited or a relay allowance state in which the relay of the communication data is allowed. When the destination port, the relay process portion discards the received communication data without saving the received communication data.