PROBLEM TO BE SOLVED: To provide a transmission system which maintains connection of the entire link and has enhanced fault resistance by escaping from a fault having occurred in partial lanes, using only normal lanes, and reducing communication capacity, in multi-lane transmission in which the number of lanes is changeable.SOLUTION: In the transmission system including a transmitter, a repeater and a receiver, the transmitter and the repeater are connected by a first transmission path, the repeater and the receiver are connected by a second transmission path, and the transmitter, the repeater and the receiver include virtual lanes. The transmitter divides transmission data into data columns of a number of usable virtual lanes on the basis of using lane information. The repeater monitors each transmission lane of the first transmission path and a fault of each virtual lane. The receiver monitors each transmission lane of the second transmission path and a fault of each virtual lane, determines a usable virtual lane, transmits the using lane information to the transmitter, and restores the divided data columns to the transmission data.