Abstract: A double-walled spiral pipe in accordance with the present invention is composed of an outer wall 10 having a cylindrical shape, which is prepared by winding spirally a coated steel plate 11 having corrugations 12; and an inner wall 20 having a cylindrical shape, which is contacted with the wave bottom of corrugations of said outer wall 10, and can contracted or elongated depending upon a change of the pitch of the corrugations of said outer wall 10. The inner wall 20 having a cylindrical configuration is installed to be contacted with the wave bottom of corrugations of the outer wall 10, and functions to drain a sewage, etc. The inner wall 20 has a semi-circular portion which is formed at the point of the wave bottom of the corrugations of the outer wall, and a plane surface is formed between the semi-circular portions.