An apparatus includes an image sensor unit, a retaining member configured to retain the image sensor unit on a photographer side and to retain an optical member on an object side, a first sealing member configured, when the image sensor unit is mounted on the retaining member, to form a closely sealed space by sealing between the image sensor unit and the retaining member, the first sealing member being provided on the photographer side of the retaining member, and a second sealing member configured, when the optical member is mounted on the retaining member, to form a closely sealed space by sealing between the optical member and the retaining member, the second sealing member being provided on the object side.