PURPOSE: To attain power application of large current without increasing the diameter of wire by constituting a filter for separation of a harmonic noise generator and for common installation of same kind systems by a ferrite core and a capacitor loaded to a power line.

CONSTITUTION: In a high frequency signal transmission system where same kind of systems are installed together by using a line filter, the line filter 4 is constituted with the capacitor 9 and the ferrite core 8 between power lines 10. Thus, a high frequency signal is attenuated by the capacitor 9. The ferrite core 8 prevents the reduction in the line impedance to the high frequency signal. In a high frequency signal transmission system having a device generating high frequency noise, a line filter 12 is constituted by the capacitor 8 connected between terminals 14, 14 of a local switch 13 at the side of a device 11 being high frequency noise source and the ferrite core 8 connected to the opposite side.