To completely screw a lag screw to a wooden structural member by reinforcing a deep female screw hole formed on a wooden structural member by a solidified layer of an adhesive, increasing screw coming-off proof strength, eliminating axial looseness of a male screw with the female screw.

A pilot hole 3 is formed by a drill having an outer diameter of a size not smaller than a root diameter of a lag screw 1. A tap of a size having a screw pitch identical to that of the lag screw 1 and a root diameter and an outer diameter not smaller than those of the lag screw is erected on the pilot hole 3. The tap is moved backward while disturbing not only crude springwood but also fall wood on a cylindrical wall surface between spiral grooves formed on the pilot hole 3. An adhesive is injected in a part in the vicinity of an opening of a tap extraction hole. The adhesive 7 is pushingly spread in the tap extraction hole by a tip part of the lag screw, and the adhesive is filled to form an adhesive solidifying layer between the tap extraction hole 6 and the lag screw 1.