PURPOSE: To carry out the corrected bending without causing trouble and to improve corrected precision, in a method for correcting the relative positional relation between the positions of both ends of a bent pipe by applying corrected bending to the bent pipe to which scheduled bending is already applied.

CONSTITUTION: A relative positional relation is measured between the positions of both ends of a bent pipe W; based on its result, as correction information necessary for carrying out bending to correct the actual relative positional relation, a corrected bending position different from a scheduled bending position and a corrected bending quantity that should be applied to the bent pipe W at that corrected bending position are each separately determined; and the corrected bending is thus applied to the bent pipe W at the determined corrected bending position and for the determined corrected bending quantity.