Data transmission system, transmitter and data transmission control method

A first transmitter transmits input data through a plurality of paths belonging to a path group. A second transmitter receives the data transmitted from the first transmitter through the plurality of paths, temporarily stores an amount of the data corresponding to a phase difference between the plurality of paths in a first buffer to absorb the phase difference, and outputs the data, whose phase difference has been absorbed, through a second buffer. When a path is deleted from the path group, the first transmitter reduces a data rate for data transmitted from the first transmitter to the second transmitter, and then deletes the path from the path group.