A coupler for a corrugated pipe that is provided with a sealing member mounted inside a fastening member and made of a softer metal material than the corrugated pipe, thereby preventing the fastening member from being damaged due to the fastening force of a cap nut, and that is provided with a grounding portion formed at the front portion of a metal sleeve in such a manner as to enter a coated layer of a composite member and to be grounded to a metal braided net of the composite member when the cap nut is fastened, thereby protecting the corrugated pipe from lightning.