Abstract: A cylindrical support portion is provided on a wafer pump case to surround a rotary shaft, and a cylindrically formed power transmitting rotary wheel surrounding the support portion is integrally coupled to an outer end of the rotary shaft which protrudes outwardly from the support portion. A bearing means is interposed between an inner surface of the power transmitting rotary wheel and an outer surface of the support portion. A plurality of sealing members disposed concentrically with the bearing means are interposed between the rotary shaft and an inner surface of the cylindrical support portion at a location axially outwardly spaced from the mechanical seal, and a grease is filled between the sealing members. The water pump structure not only improves the sealing property of the sealing members by providing the sealing members at a location in which the deflection of the rotary shaft is smallest, but also increases the retaining property for the grease between the plurality of sealing members.