To realize a structure capable of taking out respective studs 11 from respective holes 10 without disassembling a bearing unit for supporting a wheel and sufficiently ensuring endurance life of a first bearing part in a structure that pitch circle diameter PCDs of the respective studs are made to a range of 100-205 mm and pitch circle diameter PCD1 of the first bearing part is made larger than pitch circle diameter PCD2 of the second bearing part.

A PCD ratio (PCD1/PCDs) of the respective studs 11 and the first bearing part is made to 0.7 or lower. By adopting this constitution, the above problem is solved.