A focus detection device for an image forming optical system, comprising: a micro-lens array constituted with a plurality of two-dimensionally arrayed micro-lenses; a light-receiving element array for receiving an image formed by the image forming optical system, wherein the light-receiving element array includes a plurality of light-receiving elements receiving a light flux from the image forming optical system via the micro-lenses, the plurality of light-receiving elements being two-dimensionally disposed in correspondence to each micro-lens; characterised in that the focus detection device further comprises: an image generating means for generating image information regarding the image based upon output signals from the plurality of light-receiving elements; a characteristics extraction unit that detects a characteristic feature of the image represented by a quantity related to a predetermined contrast value; an area setting means for setting a calculation area for detecting a focus adjustment state of the image forming optical system, based upon the image information, the calculation area being set at a position within the image corresponding to a position at which the characteristic feature is detected; and a focus detection means for detecting the focus adjustment state based upon the output signals from the plurality of light-receiving elements corresponding to the micro-lenses within the calculation area set by the area setting means; wherein the focus detection means detects the focus adjustment state based upon an image shift quantity of a pair of the images formed by the light fluxes passed through different pupil areas at the image forming optical system. a micro-lens array constituted with a plurality of two-dimensionally arrayed micro-lenses; a light-receiving element array for receiving an image formed by the image forming optical system, wherein the light-receiving element array includes a plurality of light-receiving elements receiving a light flux from the image forming optical system via the micro-lenses, the plurality of light-receiving elements being two-dimensionally disposed in correspondence to each micro-lens; characterised in that the focus detection device further comprises: an image generating means for generating image information regarding the image based upon output signals from the plurality of light-receiving elements; a characteristics extraction unit that detects a characteristic feature of the image represented by a quantity related to a predetermined contrast value; an area setting means for setting a calculation area for detecting a focus adjustment state of the image forming optical system, based upon the image information, the calculation area being set at a position within the image corresponding to a position at which the characteristic feature is detected; and a focus detection means for detecting the focus adjustment state based upon the output signals from the plurality of light-receiving elements corresponding to the micro-lenses within the calculation area set by the area setting means; wherein the focus detection means detects the focus adjustment state based upon an image shift quantity of a pair of the images formed by the light fluxes passed through different pupil areas at the image forming optical system.