To provide a tool having excellent wear resistance and strength in the machining of an extremely difficult-to-work sintered metal.

The ultrafine-grained cubic BN sintered compact has a composition which consists of 40-70 wt.% cubic BN and the balance binder phase consisting of at least one kind among the group IVa, Va an VIa elements of the periodic table, Al, the carbides, nitrides and bodies thereof, the mutual solid solutions thereof, and the mixtures thereof. Further, the grain size of cubic BN is made to 0.01-0.40 μm, and the average value of the thickness of the binder phase is made to 0.10-0.70 μm. This sintered compact is joined by metal to a base material and coated with a hard film.