To make the tip parts of a central cone and others which are fitted to the end of a rotary cutting tool having a cutting blade of high hardness sintered body resistant to breakage.

A boring cone D1 for wood working is cut out from an intermediate product in which an end part material formed by sintering a rigid backing layer L1, a high hardness sintered body layer L2, and a rigid backing layer L3 integrally is joined to a shank material by brazing. Namely, a central cone 10 is formed from a cemented carbide, round bristle draw blades 7, 8 and a bottom blade 9 are formed from a high hardness sintered body containing diamond particles and cubic boron nitride particles, and a supporting base material is formed from a cemented carbide.