To optimize a coefficient of friction of a friction material and to lengthen the life by constituting the friction material in contact with a rotary body by polyamide based elastomer stipulated to a range of specified bending elastic modulus.

A cylindrical projecting part 4f formed on a rear cap 4d of a photosensitive drum 4 is made of steel products. On an outer peripheral surface of the rear cap 4d, a resin brake pad 25 is pressed by elastic force of a spring 26, thereby braking force for a rotating direction of the photosensitive drum 4 is obtained and rotary fluctuation of the photosensitive drum 4 caused by disturbance from a driving system of the photosensitive drum 4 is prevented from generating. The brake pad 25 is formed by polyamide based elastomer and a bending elastic modulus of the elastomer is set to a range of 100 to 50 MPa. As a result, a high value of a coefficient of friction of about 0.4 to 0.5 is obtained and sufficient braking force can be obtained when a friction material is used as a braking device of the photosensitive drum 4.