A rotary body protecting apparatus includes first and second rotary bodies, a cover, a cover detection unit, an optical detector, and a control device. The second rotary body is arranged in the same axial direction as that of the first rotary body and rotates while opposing the first rotary body. The cover opens/closes an opposing position of the first second rotary bodies. The cover detection unit detects a closed state of the cover. The optical detector is close to the opposing position of the first and second rotary bodies and arranged in the vicinity of the ends of the first and second rotary bodies. The optical detector includes a light-projecting portion which projects light in the axial directions of the first and second rotary bodies, and a light-receiving portion which receives the light from the light-projecting portion. The control device stops rotation of the first and second rotary bodies when the optical detector detects that the light-receiving portion does not receive the light from the light-projecting portion. The control device performs one of control of disabling the optical detector and control of invalidating a detection output of the optical detector when the cover detection means detects the closed state of the cover.