To easily move wall side flooring by fixing an inverse L-shaped locking piece to a nut thread-mounted on a bolt having a seat plate and a spanner locking part on both ends.

A seat plate 2 is installed on one end of a bolt 1 for thread- mounting a nut 3, a nut 4 is welded to the other end, a locking piece 7 for arranging a downward projecting part 7a in a seat plate 2 side end part is fixed to a lower part of the nut 3, and a plate member 9 is fixed to an under surface of the locking piece 7 to constitute a flooring installing tool A. At execution work, the tool A is arranged on wall 11 side flooring 6, and the projecting part 7a is locked on a wall side side surface of the flooring 6. Next, the nut 4 is rotated by a spanner 13, a wall 11 is pressed by the seat plate 2, and the flooring 6 locked on the locking piece 7 via the nut 3 is moved in the direction for separating from the wall 11 to eliminate clearance C with flooring 12. Thus, the clearance between the flooring can be easily eliminated, and since the flooring is not struck by a hammer as usual, damage can be prevented.