To effectively reduce a noise on a power line in a wide frequency band and to effectively decrease not only a continuous noise but also a sudden noise.

A power line noise filter 10 detects a change of a current at conductive lines 1a, 1b of the power line 1 by a detector 11 and hence detects the noise of a common mode of current properties on the line 1. A reverse phase signal generator 12 generates a reverse phase signal as a signal having a reverse phase to the noise detected by the detector 11. Further, the change of the same current corresponding to the reverse phase signal is given to the two lines 1a, 1b of the line 1 for the two lines 1a, 1b of the line 1 by an injection circuit 13. Thus, the noise of the common mode of the current properties on the line 1 is cancelled.