The present invention provides a differential signalling cable and a transmission cable assembly using the same, and a production method for the differential signaling cable. In the differential signaling cable, offset, differential common-mode conversion amount and transmission waste are reduced together, EMI performance is good, characteristic impedance for determining transmission characteristics is gradually changed, stable production can be performed, the cable is easily mounted on a substrate or a connector, deterioration of electric characteristics of a mounting section is less, and deterioration of signal waveshape is less. In the differential signaling cable comprising: a pair of signal conductors (2) provided in parallel, an insulator (3) which covers the periphery of the pair of signal conductors (2) in a batch, and a shield conductor (4) provided on the outer periphery of the insulator (3), an interval between the pair of signal conductors (2) is specified so that even-mode impedance becomes 1.5 to 1.9 times odd-mode impedance.