Abstract: A construction is adopted in which an annular spacer 27 is held between first and second inner races 2a, 2b. An internal clearance in a double-row bearing unit is measured in a middle step of assembling work of a wheel supporting bearing assembly, and in the event that a resultant measured value does not become a proper value, an axial dimension of the spacer 27 is adjusted, so that the internal clearance becomes the proper value. Thereafter, the assembling work is made to continue until the assembling work is completed. A problem which is to be solved by the invention is solved in the way described above.