To achieve both miniaturization and positioning accuracy improvement of a motor unit having a rotation detecting part and driving a lens.

A lens barrel includes: a motor for driving an optical element; rotation detecting means installed on a rotating shaft of the motor; a mounting member fixed to the motor; two or more parts to be positioned provided on the mounting member; a first housing holding the motor; a notch provided in the first housing and overlapped with a position of the motor; positioning parts installed at two or more points across the notch and closer to a notch opening than the rotating shaft center of the motor; rotation detecting means which detects the rotation of a rotation detecting target member; and a second housing which holds the rotation detecting target member, is installed at a position overlapped with the notch, and does not interpose other pars between it and the mounting member.