An electronic image pickup apparatus comprises a photographic optical system; solid state image pickup devices disposed on a plant where a subject image formed by subject beams which have passed through the photographic optical system is formed; a main mirror disposed between the photographic optical system and the solid state image pickup devices, wherein a part of the main mirror is formed of a half mirror to divide the subject beams which have passed through the photographic optical system into an observing beam and a focus detecting beam; a sub-mirror for reflecting the subject beam which has passed through the part of the main mirror; a focus detecting optical system for forming an image of the subject beam reflected by the sub-mirror on a partial area of the solid image pickup devices; and an electrical circuit for outputting focus detecting information based on image signals of the partial areas of the solid image pickup devices. The structure provides an electronic image pickup apparatus which contributes to the down-sizing of the apparatus and to the reduction of production cost by eliminating an image pickup device which is dedicated for focus detection.