To extract a value corresponding to a noise in a signal from the signal by evaluating only the absolute value of difference, namely, only absolute difference between a certain line and a correspondent line in the next field or frame.

A delay means 10 stores a signal section found for measuring the noise for the unit of a field or a frame. An absolute difference calculating means 20 finds a differential signal 23 between a signal 12, for which an input video signal is delayed for one field or one frame by the delay means 10, and a current input signal 11 and its absolute value 27 is calculated by an absolute means 24. An accumulator 40 adds all the absolute difference calculated for each field or frame and a total value 45 is outputted as a value expressing the noise in the current field or frame of the signal and used for controlling a noise reduction filter. A difference calculator 22 and the accumulator 40 are controlled by a gate pulse 55 prepared by inputting a horizontal synchronizing signal 51 and a vertical synchronizing signal 52 of the video signal through a measuring window circuit 50.