A collapsible type optical unit is described that is capable of moving its optical system between a working position and a retracted position as well as an image-pickup apparatus including the optical unit. The optical unit and the image-pickup apparatus are capable of acquiring lens-position information by detecting a position of a lens barrel supported to be movable with respect to a fixed barrel. The collapsible type optical unit includes a second group lens frame movable along a direction of its optical axis with respect to a fixed ring and rear barrel, and a solid-state image-pickup device provided behind the second group lens frame, in which on the movable second group lens frame, a position-detecting means for detecting a position of the second group lens frame is provided.