A controller of a tag conversion apparatus configured holds tag conversion information associating addresses of communication apparatuses and information on tags of tagging schemes for network separation, analyzes a frame input from one of the plurality of ports and determine a current tagging scheme of the frame, determines a tagging scheme associated with a destination address of the frame based on the tag conversion information, and converts the frame to a frame of the tagging scheme associated with the destination address based on the tag conversion information when the tagging scheme associated with the destination address and the current tagging scheme are different.