A data transfer system transfers data via a plurality of signal lines and controls to select the signal lines to adapt reduction and lane reversal. The signal line control unit has a signal creation unit that creates a first selection signal when the signal lines are reduced according to the abnormal detection from the abnormal detection unit, and a signal output unit that outputs a second selection signal when a connection of the second selection signal indicating that any one or both signal line of a second pair of signal lines is changed in case of a lane reversal that connects a plurality of signal lines in a down order from a highest bit to a lowest bit of a sending device side with a plurality of signal in a up order from a highest bit to a lowest bit of a reception device side.