A bearing device assembly includes a water pump shaft supported by a rolling bearing, and a plulley seat press fitted to one end of the water pump shaft. A recess or recesses in the form of a ring-shaped groove, a spiral-shaped groove, and a groove extending in the axial direction of the shaft, or the like are formed in at least one of the peripheral surface of the one end portion of the water pump shaft and the inner surface of the pulley seat. The recess prevents formation of an oil film on the fitting surface between the water pump shaft and the pulley seat at the time of press fitting the pulley seat, and also allows the remaining oil on the fitting surface to flow into the recess.