An image processing apparatus includes: a characteristic value calculation unit calculating a block luminance average value, which is an average value of luminance values in each of spatial blocks obtained by dividing an input image in a space direction, and a block luminance dispersion, which is a dispersion of the luminance values in each of the spatial blocks; and an edge-preserving smoothing unit calculating a general luminance value of pixels of the input image by setting a value obtained by approximately calculating a weighted average value of the luminance values of a noticed block containing noticed pixels of the input image, on the assumption that a distribution of the luminance values of each of the spatial blocks conforms to a Gaussian distribution based on the block luminance average value and the block luminance dispersion of each of the spatial blocks, as the general luminance value of the noticed pixels.