An image forming apparatus including a rotatably driven transfer drum is provided. The transfer drum includes a main body and a dynamic vibration reducer. The dynamic vibration reducer includes an inertia pipe having an inertial moment, and at least one element connecting the inertia pipe to the interior of the main body so as to provide a spring-like property and a damping property therebetween. The apparatus dynamically reduces vibrations in a predetermined frequency band, such as that of the natural frequency of a specific gear, or the natural frequencies of an entire drive mechanism. In particular, the apparatus reduces vibratory peaks generated during the operation of the image forming apparatus.