A focus detecting apparatus includes: a micro lens array having plural micro lenses; a photo-detector having detecting elements corresponding with the micro lenses and receiving light flux from an optical system via the micro lenses; a center detector detecting a center position of each micro lens; an image generator generating an image from the center position of each micro lens and photo-detector output; a contrast detector detecting contrast values of an image signal of the image; a calculator calculating an integrated value by accumulating contrast values for each of plural partial images from the image; and a focus detector detecting focus adjustment status by calculating an image shift amount caused from light fluxes passed through different pupil areas of the optical system based on output of the detecting elements corresponding to the partial images from which a maximum value is obtained among the integrated values calculated by the calculator.