A bearing unit has four rolling bearings adjacently disposed in an axial direction, each rolling bearing including an inner race, and outer race, and rolling elements interposed between the inner and outer races. A shaft is fitted to the inner races, and a sleeve has a fitting hole into which is fitted the outer races. The inner races or the outer races are brought into contract with each other in the axial direction to preload the rolling bearings. The inner races or the outer races of the rolling bearings at both axial ends, which are brought into contact with the inner races or the outer races of adjacent rolling bearings, are fixed to the sleeve, and the outer races of the central two rolling bearings form a radial gap between confronting surfaces of the sleeve and the outer races or between confronting surfaces of the shaft and the inner surfaces.