PROBLEM TO BE SOLVED: To determine a contrast medium area by taking a manner of temporal fluctuation of a pixel value into consideration.SOLUTION: An image processor includes a generation part for generating a first image on the basis of a plurality of frame images included in a radiation moving image, a measurement part for measuring a temporal change of a pixel value at a corresponding pixel position in the plurality of frame images, and processing means for performing processing for changing the pixel value at the pixel position in the first image by using the measured pixel value to acquire a second image.
