To provide a unit assembly having a working hole high in precision even when a hollow hole is deformed by caulking, etc. and its broaching method.

The working hole 14b is worked in the hollow hole by moving a helical tooth groove broach 31 in the vertical direction by placing the unit assembly 1 integrally assembling a bearing 12 having a plurality of balls 17 and an outer ring 16 on the outer peripheral side by irreversibly deforming a part 14 which the hollow hole 2 has on a horizontal table 36 through a tool 37 so that the hollow hole becomes vertical. The working hole 14b is drilled at broaching speed of more than 10m/min and less than 80m/min dry or by applying a small amount of mist by removing chips attached on a broach tooth by a chip brush 32 arranged on a lower surface of the tool or in the inside 38 of the tool and a plurality of air blow nozzles 33 arranged in the proximity of and against the broach tooth 31a of the broach below the tool.