A transmission system includes a transmission device and a reception device connected with each other via two lines. When the transmission device switches a line, used for transmitting VLAN traffic, from a first line to a second line, the transmission device transmits the VLAN traffic to the second line by switching the line after transmitting a post-switching message to the first line. The reception device includes a first buffer which stores the VLAN traffic received from the first line and a second buffer which stores the VLAN traffic received from the second line. When the reception device receives the post-switching message from the first line, the reception device starts reading of the VLAN traffic from the second buffer after reading the entire VLAN traffic stored in the first buffer.