An image processing apparatus according to the present invention comprises a histogram generating section for generating a histogram by counting a frequency value for each gradation of a predetermined number of gradations as brightness distribution of input image data, a distribution processing section for distributing a count value of the histogram to adjacent gradations, a cumulative histogram generating section for generating a cumulative histogram by accumulating the histograms obtained by the histogram generating section from a low gradation side, and a gradation correction processing section for performing contrast correction by using the cumulative histogram, wherein the distribution processing section fixes a distribution amount to the predetermined number of gradations when distributing the count value to the adjacent gradations.