PURPOSE: To improve the joining strength by drilling a conical hole in the end part of a ceramic shaft and providing a similar projection for a metal shaft so as to mate them with a care that any air in the hole will not be trapped during the mating service and bonding agent involves no air.

CONSTITUTION: A ceramic shaft 53 is short and is to be mated with a metal shaft 54 at the border with a bearing part. The ceramic shaft 53 has a conical hole 53a cut in the end face thereof, said hole having the spherical bottom. A metal shaft 54 has a spherically bottomed conical projection 54a formed at one end exceeding the bearing 31. Both of their contours are similar. The mating part is exposed to high temperature due to vicinity to an exhaust gas passage. The internal face or the ceramic face of the conical hole 53a has a metallizing layer and the joined part is then brazed at a temperature higher than that to which the face is exposed when a turbine is driven.