An image processing apparatus (100) includes a synthetic image acquirer (24) for acquiring a plurality of smoothed images different from each other, in which noise components have been smoothed on an image to be processed, and that is operable to perform weighted synthesis of the smoothed images based on pixel value differences between a pixel value of a pixel of the image to be processed and pixel values of pixels of the acquired smoothed images, in which a positive and a negative have been taken into consideration.