An HGW mobile device 20 can perform data communication on the basis of a plurality of wireless communication methods with different theoretical maximum transmission speeds, i.e., on the basis of a mobile wireless communication method and a wireless LAN communication method. Since the HGW mobile device 20 is provided with a mobile wireless communication unit 210 and a wireless LAN communication unit 250, it is able to relay data transmission between an external network 10 and a client terminal 30. A transmission speed initializing unit 230 sets a value according to a theoretical maximum transmission speed of the wireless communication method with the slower theoretical maximum transmission speed, i.e., the theoretical maximum transmission speed of the mobile wireless communication method, as an initial transmission speed for the wireless LAN communication unit 250 to first start wireless LAN communication with the client terminal 30 on the basis of the wireless LAN communication method.