PURPOSE: To facilitate the advance and retreat of an upper unvil and to make the complicated controlling unnecessary, by constituting a structure so that an extending part reaches the other roller means for feeding the anvil while holding the center of gravity of an upper anvil between one roller means for feedint the anvil and a guide wheel.

CONSTITUTION: When an upper anvil 3 is advanced into a through-hole 2a of a ring 2, a guide wheel 18 is drived by a motor as a trailing wheel, and if the upper anvil 3 is moved in the direction of the through-hole 2a, an extending part 3a reaches another feeding roller means 17a. After the extendint part 3a reaches the feeding roller means 17a, the upper anvil 3 advances rapidly to the prescribed position being driven by both the roller means 17a, 17b. In this state, the guide wheel 18 separates perfectly from a rail 19 and the weight of the upper anvil 3 is supported by both the roller means 17a, 17b.