An absolute coordinate acquisition method is an absolute coordinate acquisition method for acquiring absolute coordinates of an underground pipeline, the method including: a marking step S101 of setting a plurality of reference points on a road surface and setting a measurement point on a pipeline installed inside an excavated ditch; a measurement step S102 of measuring absolute coordinates of the reference points; a relative position calculation step (S103 to S105) of calculating relative positions of the reference points and the measurement point to a reference position; and an absolute coordinate calculation step S106 of calculating absolute coordinates of the measurement point based on the absolute coordinates of the reference points and the relative positions of the reference points and the measurement point.