Apparatus and method for realizing a processing with which a pixel gravity center control can be conducted when a pixel number reduction image is generated in an image pickup apparatus. A pixel unit configured to output a pixel addition signal obtained by adding output pixel signals from pixels having different sensitivities to each other and a pixel information synthesis unit configured to execute a weighted addition processing of multiplying plural pixel addition signals output from the pixel unit by a previously set gain and calculate a configuration pixel value of a pixel number reduction image where a total number of pixels is lower than a number of pixels of the pixel unit are provided.