Abstract: A shaft balancer is provided for automatically correcting an unbalanced condition in a rotating shaft and thereafter maintaining the rotating shaft in a balanced condition. The shaft balancer comprises a housing having an outer rim and means for securing the housing to the shaft so that the rim is concentric with the axis of rotation of the shaft. An annulus, constructed of a flexible material, is positioned within the housing and includes a base and an outer slotted rim. The base of the annulus is secured to the housing so that the slotted rim is concentric with the shaft. In addition the slotted rim is spaced radially inward from the housing rim thus forming an annular raceway adapted to receive a plurality of ball members for rotation therein. A floating inertia ring is secured concentrically across the open end of the annulus slotted rim and is radially movable within the housing.