To provide an expanded hole drilling device, a component for the expanded hole drilling device, and an expanded hole drilling method, capable of expanding the diameter of a previously bored hole without causing decentering.

The expanded hole drilling device 10 is provided with a drill holder 22 attached to a drill grasping part 18 in place of a drill 16 and grasping the drill 16, and a centering attachment 24 with a conical tip, which is attached to the drill holder 22. The expanded hole drilling method comprises steps for: arranging bored work on a table 14 in a displaceable manner; inserting the tip of the centering attachment 24 in a bored hole for centering the bored hole; fixing the centered work to the table 14; boring the work to expand the hole by the drill 16 after removing the centering attachment 24.