PURPOSE: To remove noise in the case of superimposing fine noise by outputting any specified value from an adder corresponding to the absolute value of difference between median and (N+1)th signal levels.

CONSTITUTION: The f-fold average value of the signal level of an input signal is outputted from a low-pass filter part 31, the median g-fold signal level is outputted from a median filter part 32, and the h-fold (N+1)th signal level is outputted from a signal processing part 33. An adder 34 adds these outputs. The adder 34 is set so as to output a smoothed value when the absolute value of difference between median and (N+1)th signal levels is smaller than a prescribed first level and so as to output median when it is larger than a second level. Thus, this device is operated as the low-pass filter to the fine noise of a small amplitude and operated as the median filter to the pulse signal of a large amplitude. Thus, noise can be removed even to a signal superimposed the fine noise of which level is periodically changed.