In a demultiplexer, a finite search length and a finite jump length are set in a packet header detection section. The packet header detection section skips from a transfer start position of a multiplexed stream according to the set jump length and then searches for a start code included in a packet header which is to be detected through a range designated by the search length. A payload separation section separates payloads included in the multiplexed stream based on detection results of the packet header detection section.