Abstract: When laying a conduit comprised of double-wall pipes A, each of which comprises inner pipe 1 and outer pipe 2, the smooth propulsion of double-wall pipes is possible by injecting lubricant into a space between the outside of double-wall pipes and the ground on a scheduled line along which conduit B to be laid is divided into section, each having a given length based upon the distance over which the effect of the lubricant can be maintained. Lubricant is injected from the double-wall pipes which is to be positioned at the heads in the respective sections 1 to n of supply pipes 3 which are provided between inner pipe 1 and outer pipe 2 of double-wall pipe A. Supply pipes of double-wall pipe A which has been propelled are connected with supply pipes of a new double-wall pipe, wherein the number of supply pipes connected with each other is determined for the respective sections. Lubricant is supplied from the upstream side and from the downstream side of the propelling direction to double-wall pipes.