An image processing apparatus, comprises: an image-obtaining unit configured to obtain a visible image and an infrared image; a luminance obtaining unit configured to obtain a luminance of the visible image; a determining unit configured to determine, based on the luminance obtained by the luminance obtaining unit, a combining ratio between the infrared image and the visible image for generating a combined image obtained by combining the infrared image with the visible image; a combining unit configured to combine the infrared image with the visible image based on the combining ratio determined by the determining unit; and a correcting unit configured to correct the combining ratio such that an amount of change in the combining ratio does not exceed a threshold value, in a case where the amount of change in the combining ratio exceeds the threshold value.