An imaging unit includes an incident-side reflecting surface provided in a casing and reflects object-emanating light, entering the casing in a thickness direction thereof, along a lengthwise direction of the casing; a movable lens group movable along the lengthwise direction of the casing; an exit-side reflecting surface reflecting the light in the thickness direction of the casing; an image sensor provided in the casing and receiving the light from the exit-side reflecting surface; and a plurality of light shield frames provided in the casing between the movable lens group and the exit-side reflecting surface, the light shield frames being arranged in the lengthwise direction of the casing and moving in the lengthwise direction of the casing when the movable lens group performs a power-varying operation.