A rotating body support device includes a shaft, a bearing, a mounting member, and a protruding part. The shaft serves as a rotating shaft which rotates or a fixed shaft during rotation of a rotating body. The bearing includes an inner peripheral part for supporting the shaft and an outer peripheral part disposed at an interval in a radial direction relative to the inner peripheral part. The mounting member includes an insertion part on which the outer peripheral part is mounted, and supports the bearing. The protruding part is provided to protrude from one of a peripheral face of the shaft and the inner peripheral part of the bearing in the radial direction along a peripheral direction of the rotation. Moreover, the protruding part comes into contact, along the peripheral direction, with the other one of the peripheral face of the shaft and the inner peripheral part of the bearing.