An apparatus and a method for multilateral one-way communication are provided. The apparatus includes a one-way input module unit, detachably mounted to a plurality of slots formed in a rail, for receiving data from an external transmission host and for transmitting the received data to an internal network through one-way communication; a one-way output module unit, mounted detachably to the plurality of slots formed in the rail, for transferring data of interest to an internal network through one-way communication, and transmitting data of interest to an external reception host, and a two-way module unit, mounted detachably to the plurality of slots formed in the rail, for performing data communication between the transmission host and the reception host in a bidirectional mode.