To enable adjusting a hole length of the top end punch for each billet so as to obtain a most suitable engagement.

A top end punching apparatus of centering machine provided with a clamping apparatus 4 to clamp the top end section of the billet 1 placed in one-way side of the roller table 2 on which a billet 1 is mounted, and a top end punch 5 to open a punch hole in an axial position of the top end surface of the billet 1 whose top end section is clamped by the clamping apparatus 4. A detection sensor 5c to detect a traveling distance of the top end punch 5 is provided. Accordingly, a top end punch hole can be opened go as to obtain the most suitable engagement for the targeted billet.