Although an area type focus detecting device for performing phase difference detection type multi point autofocus is used for high speed high precision autofocus of multi points in a wide region, there is a problem of cost increase due to the increase of the chip area. In accordance with the present invention, the photoreceiving area of a specific pixel in an area sensor is made larger than the photoreceiving area of other pixels in the same area sensor. Thus, because the sensor sensitivity is improved and the increase of the chip area is suppressed to a minimum level, a low cost high precision area type focus detecting device can be provided.