A transmitting system includes a variable-length packet multiplexing apparatus and a transmission slotting apparatus. The variable-length packet multiplexing apparatus generates a variable-length packet. The transmission slotting apparatus stores the variable-length packet in slots forming transmission main signals. The transmission slotting apparatus includes a capacity calculator, an extractor, a remainder calculator, a selector, and a slot information multiplexer. The capacity calculator calculates a data capacity of the transmission main signals for one frame. The extractor extracts a byte number of the variable-length packet. The remainder calculator calculates a remaining capacity of the transmission main signals. The selector stores a predetermined data sequence in a region left in the slots, and outputs the slots storing the data sequence. The slot information multiplexer multiplexes slot information and the slots output by the selector.