To provide a preload device for a bearing capable of controlling the preload of the bearing without using an auxiliary driving means such as a fluid pressure supply means.

This preload device for bearing 2, in which inner ring spacers 3 and outer ring spacers 9 are disposed alternately in a housing 4 and supports a rotating shaft 1, includes a flange 5 fixed on one end of the housing 4, a bearing cover 7 fixed at one end of the housing 4, a bearing cover 7 supported at the other end so as to be capable of moving in the axial direction, and a bellows-type leaf spring 10 formed so that its inner periphery may touch the outer peripheries of the bearing 2 and the outer ring spacer 9 and both ends in the axial direction may touch the flange 5 and the bearing cover 7.