In a mobile network system composed of plural mobile networks and a home agent, the home agent inquires mobile routers in a mobile network whether or not a terminal is connected, if detecting the absence of the terminal, when data addressed to the terminal arrives at a home network of the terminal in the mobile network. Responding to this inquiry, the mobile routers search whether or not the terminal is connected to the own mobile networks. If the terminal is connected, the mobile routers inform the home agent of the presence of the terminal. When receiving this notice, the home agent transfers data addressed to this terminal to a mobile router as a notice source. This process, even if a terminal moves to a mobile network having a same network prefix as that of the home network, allows transferring a packet accurately to the terminal.