A data transfer apparatus includes a transmitting unit, a transmission controlling unit, and a generating unit. The transmitting unit transmits transmit data over a transmission channel having a plurality of lines, such that the transmit data are assigned to the plurality of lines by information unit of the transmit data, the information unit. The transmission controlling unit appends control data to transfer data to be transferred to a receiving side to compose the transmit data, the control data being for controlling transmission and reception of the transfer data. The generating unit obtains information about the number of the lines. The generating unit determines, based on the number of the lines and the number of information units of the control data, the number of information units of the transfer data that makes the number of information units of the transmit data integral multiple of the number of the lines.