PURPOSE: To provide an electrode screw-in tool capable of easily demounting it from an electrode without requiring large rotary driving force.

CONSTITUTION: The upper part of a plug 2, in which a male screw part 6 to be screwed in the connection hole 4 of an electrode upper end part is provided on the lower part and which is composed being divided into plural divided pieces 24 via slot-state gaps extended in a vertical direction, is diameter- expandably/contractibly supported in an outer tube 7. The whirlstop member of a plug 2 is provided on the outer tube 7, and the lower part of a hanging frame 10 having a hanging hand 1 is fixed to the outer tube 7 at a position on the center axis line 8 of the plug 2. As a drive device diameter-expandably/ contractibly driving the plug 2 by driving the divided pieces 24, this fitting is provided with a wedge drive device 17 driving a wedge 16 engaged with a tapered hole 15 provided on the plut 2, and a spring interposed between the divided pieces 24 and the outer tube 7.