An image generation apparatus is provided with: a resolution sensitivity conversion unit which generates different weight-averaged images by performing convolution operations on the infrared image with plural different weighted-filter images, and generates a resolution-sensitivity-converted image by adding luminance differences between the weight-averaged images to luminance values of the infrared image; a luminance shift calculating unit which sets the most frequently appearing luminance value of the resolution-sensitivity-converted image to an intermediate value in an enlarged range and as an intermediate luminance value, and generates a luminance-shifted image obtained by linearly shifting luminance values of the resolution-sensitivity-converted image in such a manner that the shifting corresponds to the intermediate luminance value and the enlarged range; and a luminance arithmetic operation unit which generates an arithmetically processed image by performing an arithmetic operation based on luminance differences between corresponding positions of the luminance-shifted image and a reverse shifted image.