A packet communication method and a packet communication system capable of making an IPv4-compatible application operating on an information processing apparatus communicate with another information processing apparatus connected to an IPv6 network without using an address translation router. In the information processing apparatus connected to the IPv6 network, an IPv4-to-IPv6 protocol conversion control function is incorporated in a LAN driver. A protocol conversion control module receives an IPv4 packet from a protocol control module. When a send destination IPv4 address contained in a header of the packet is registered in an address translation table incorporated in the protocol conversion control module, an IPv6 address is generated to be sent onto a LAN. Unless the send destination IPv4 address contained in the packet header is registered in the address translation table incorporated in the protocol conversion control module, the IPv4 packet as received is intactly sent onto the LAN.