An apparatus and a method for equalizing a histogram are provided to obtain cumulative distribution necessary for histogram equalization by simple circuit configuration without a lot of registers. A histogram equalization apparatus comprises a memory(410) and an operation unit(420). The operation unit overwrites the first and second data read from the memory on a location of the second data of the memory(411.421). The operation unit comprises a register. The register stores and maintains the first data. The operation unit can add the first data and the second data outputted from the register. The operation unit comprises a multiplexer. The multiplexer outputs data having 1 according to a control signal and outputs the first data.
