1. An image processing apparatus for noise reduction processing of frame images or field images that are input time-sequentially, comprising a recording unit configured to record a processing target frame image or field image and previous and future frame images or field images relative to the processing target frame image or field image; a first pixel-extracting section configured to extract a plurality of pixels in a prescribed region in the processing target frame image or field image recorded by the recording unit; a second pixel-extracting section configured to extract a plurality of pixels in a region corresponding to the prescribed region in the previous frame image or field image and in the future frame image or field image recorded by the recording unit; a first distance calculating section configured to calculate temporospatial distances between a target pixel in the prescribed region extracted at the first pixel-extracting section and both the plurality of pixels in the prescribed region and the plurality of pixels in the region corresponding to the prescribed region, extracted at the second pixel-extracting section; a second distance calculating section configured to calculate inter-pixel-value distances between the pixel value of the target pixel in the prescribed region extracted at the first pixel-extracting section and both pixel values of the plurality of pixels in the prescribed region extracted at the first pixel-extracting section and pixel values of the plurality of pixels in the region corresponding to the prescribed region, extracted at the second pixel-extracting section; and a noise reduction section configured to perform noise reduction processing of the processing target frame image or field image on the basis of the temporospatial distance calculated by the first distance calculating section and the inter-pixel-value distance calculated by the second distance calculating section.