To easily assemble a rubber vibration insulator body 31 and an inertia body 32 in a rubber vibration insulator 3 for an image formation drum.

The rubber vibration insulator comprises the cylindrical rubber vibration insulator body 31 and the inertia body 32. The rubber vibration insulator body 31 is kept in close contact with the inner peripheral surface 11a of the image formation drum 1. The inertial body 32 is inserted in the inner periphery of the rubber vibration insulator body 31. An engagement projection 313 formed on the inner peripheral surface 31b of the rubber vibration insulator body 31 and having a diameter which becomes gradually smaller in the direction of insertion of the inertial body 32, and an engagement recess portion 321 formed on the outer peripheral surface 32a of the inertial body 32 are engaged with each other so that the inertial body 32 is held in the inner periphery of the rubber vibration insulator body 31.