A stereo-image photographing apparatus enabling readily, short time-span realization of lens-barrel optical-axis adjustment in left- and right-eye imaging devices is afforded. The apparatus includes: a beam splitter having an incident surface of rectangular form, on which imaging light from a photographic subject is incident, an optically functional surface that reflects first imaging light, being a portion of incident imaging light, in a direction paralleling the shorter side of the rectangular form and that passes second imaging light being the remaining portion of the incident imaging light, a first light-exit surface through which the first imaging light exits, and a second light-exit surface through which the second imaging light exits; a first lens barrel directly facing the first light-exit surface; a second lens barrel directly facing the second light-exit surface; a first imaging device mounted on the first lens barrel; and a second imaging device mounted on the second lens barrel.