A header compression/decompression apparatus that improves the throughput of an overall multilayer protocol stack at a network node. In this apparatus, an encoding section 106 compresses multilayer header information included in a protocol data unit on a multilayer protocol stack 101. A session context ID manager 112 generates a session context ID 401 which is formed by integrating information on compression of multilayer header information by the encoding section 106 and, for example, information for identifying a scheme for compressing multilayer header information.