To surely actuate a focal position detector with a simple structure by installing a focusing ring with a slid gear, a focus output shaft fixed in an optical axis direction, a brush mount ring which is rotated in accordance with the transmission of the rotation of the focus output shaft and a printed wiring board.

A focal distance is decided, then, the focus output shaft 52 is driven so as to output, then, a coupling member 54 is rotated, and also, an interlocking gear 62 is rotated through a gear train. The rotation of the interlocking gear 62 is transmitted to the focusing ring 26 through the engagement of a slide gear 64 of the output shaft 66 and a slid internal gear 70, then, a 1st lens group 10 for focusing is moved so as to focus. On the other hand, the rotation of the coupling member 54 is transmitted to the brush mount ring 84 through a focal position detection gear 80. By rotating the ring 84, a detection brush 90 installed on the ring 84 is made to slide on the hard printed wiring board 86, and a part corresponding to the focal position on a conductive pattern on the board 86 is conducted.