1. An image processing device for receiving a moving picture including a time sequence of frames, the image processing device comprising: a plurality of one-dimensional low-pass filters calculating respective low-pass filtered values using a pixel of interest and pixels aligned in different one-dimensional directions with respect to the pixel of interest, in a processing window including a plurality of pixels centered on the pixel of interest, in a frame of interest; a peripheral low-pass filter outputting, as a peripheral low-pass filtered value, a low-pass filtered value obtained using the pixel of interest and neighboring pixels thereof in the processing window; a representative value calculator for performing filtering in a time axis direction, based on a pixel value of the pixel of interest in the frame of interest and a pixel value of a pixel in a position corresponding to the pixel of interest in at least one frame other than the frame of interest, to obtain a representative value for the pixel of interest; a noise level detector for calculating absolute values of differences between the representative value and each of the one-dimensionally low-pass filtered values and outputting, as a noise level of the pixel of interest, a minimum value among those of the calculated absolute differences that satisfy a predetermined condition; an NR coefficient generator for receiving the noise level and generating a noise reduction coefficient corresponding to the noise level according to a predetermined input-output characteristic; and an NR processor for using the noise reduction coefficient to take a weighted sum of the pixel value of the pixel of interest and the peripheral low-pass filtered value.