The invention provides a differential signal transmission cable and a multi-core differential signal transmission cable capable of reducing a bit error rate by attenuating common-mode signals that propagate through a pair of signal lines. The differential signal transmission cable (10) includes first and second signal lines (21,22) arranged parallel to each other, a conductive layer (3) made of a conductor in which a current is induced when signals propagate through the first and second signal lines (21,22), and a dielectric (20) disposed between the first and second signal lines (21,22) and the conductive layer (3). The conductive layer (3) has a signal attenuating structure including a non-continuous section in which the conductor is non-continuous, the non-continuous section being located such that, among differential signal components and common-mode signal components included in the signals propagating through the first and second signal lines (21,22), the common-mode signal components are attenuated by an attenuation factor greater than an attenuation factor of the differential signal components.