A differential transmission line that has three or more signal lines and with which there is little unwanted radiation noise is provided. The differential transmission line 2 is provided with three signal lines 2a, 2b, and 2c that transmit differential signals from a differential driver IC1 to a differential receiver IC3, and the majority of the signal lines 2a, 2b, and 2c is provided in conductor layers T2 and T3 of a printed circuit board 4. The signal lines 2a, 2b, and 2c are provided with a signal line parallel segment, a signal line route length adjustment segment that is on the differential driver IC1 side and that connects from differential signal output terminals 1Ea, 1Eb, and 1Ec in the differential driver IC1 to the signal line parallel segment, and a signal line route length adjustment segment that is on the differential receiver IC3 side and that connects from the signal line parallel segment to differential signal input terminals in the differential receiver IC3, wherein the signal lines 2a, 2b, and 2c are formed such that their signal line route length adjustment segments on the differential driver IC1 side are equal in length to one another.