A double-row angular contact ball bearing for a CT scanning device includes an inner member including a pair of raceway rings. The raceway rings have positioning holes into which a positioning member is inserted, to thereby suppress radial decentering of the raceway rings. Both the raceway rings are fastened by fixing bolts. The raceway rings have opposed end surfaces, and are fastened by the fixing bolts to bring the end surfaces into abutment against each other to apply a preload at a fixed position between balls and raceway surfaces. The following relationship is set: Db/h≤0.26, where Db represents a diameter of each of the balls, and h represents a radial dimension from a center of each of the balls to an inner diameter of the inner member.