PURPOSE: To make an extended plug accurately mountable in a drilling hole by engaging an antirotation member with an expansion sleeve of this extended plug, insetting an elastic member in an interval between a bolt and a sleeve, and making an expander so as to be drawn into the sleeve with a rotation of the bolt.

CONSTITUTION: An antirotation member 3 is locked to a driver casing 19, while a bolt 10 is extended into a through hole 20 of an expansion sleeve 12, and an elastic member 21 clamping the bolt 10 to the sleeve 12 is set up in a thread ridge of the bolt 10. In this case, this member 21 is made up of a rubber ring preventing any rotation of the bolt 10 to the sleeve 12. When a driving member 2 is rotated, the bolt 10 is thread-fastened upward in an internal thread 9, and thereby an expansion conical part 11 is retracted into the sleeve 12, whereby an expansion range 14 of the sleeve 12 is expanded. In this case, this expansion range 14 is engaged with a conical undercut section 22 of a drilling hole 5.