A transmission device (4a) characterized by having a setting unit (corresponding to a LAN mapping circuit (100a)) for setting each one of radio lines (1, 2) as a radio line for transmitting a frame having a specific frame structure and a radio line for transmitting a packet, and a transmission unit (corresponding to a LAN packet dividing circuit (200a), an E1 framing circuit (300a), a LAN packet reconstruction circuit (400a), a buffer circuit (500a), a selector circuit (600a), and a multiplexing-demultiplexing circuit (700a)) for transmitting the frame and the packet using the radio lines (1, 2) in accordance with information (LAN mapping information (101a)) set by the setting unit (100a).