A packet communication system for effectively using network resources and for improving network operability. A transmission security policy database specifies the omission of header information attached when a transmission packet is capsulated, as a transmission security policy. A header-information omitting section omits the header information of the capsulated transmission packet. A packet transmission processing section adds a security header and a header for tunnel communication to the packet from which the header information has been omitted and transmits the packet. A receiving security policy database specifies that the header information has been omitted, as a receiving security policy. A header-information recovering section searches the receiving security policy database for a security policy for a received packet, and when recognizing that the received packet is a target packet from which the header information has been omitted, recovers the header information.