According to an embodiment, a multiplexing device includes: a packet generating unit which generates one or more third packets based on at least one of one or more first packets and a second packet; a main signal generating unit which generates from the third packets a main signal; an information generating unit which generates transmission multiplexing control information; a slot generating unit which generates a slot by combining the transmission multiplexing control information and the main signal corresponding to the information described in the transmission multiplexing control information having been generated a predetermined number of frames prior to the currently generated transmission multiplexing control information; and a time writing unit which writes a time in the second packet in the main signal included in the generated slot.