A signal transmission cable (10) having a conductor portion for transmitting signals and an insulator sheath (14) covering the conductor portion, and a high loss magnetic film (15) [is] formed on at least one part of the outer surface of the insulator sheath. The high loss magnetic film has the maximum complex permeability &mgr;″max in a frequency range of 0.1-10 gigahertz (GHz). An example of a magnetic composition of the high loss magnetic film is a M-X-Y magnetic composition wherein M is a metallic magnetic material selected from among Fe, Co, and/or Ni, X is an element or elements other than M and Y, and Y is F, N, and/or O, the M-X-Y magnetic composition having a sufficient concentration of M in the composition so that the M-X-Y magnetic compostion has a saturation magnetization of 35-80% of that of the metallic magnetic material M alone.