To shorten work time, to improve workability, and to enhance the connection strength between an end of an existing pipeline and an end of a new pipeline, without requiring worker's skill, in a method for connecting a new pipelines between existing pipelines built in existing ducts connected with the left and right side walls of a manhole, respectively.

In an existing manhole where cables in existing pipelines built in existing ducts connected with the left and right side walls, respectively, of the manhole are connected in the manhole, a process to be carried out includes the steps of: removing the cables present in the existing pipeline; coring the side wall of the manhole from the inside of the manhole in a portion corresponding to the existing pipeline with cables removed; inserting a new pipeline into a coring hole formed by coring from the inside of the manhole; connecting an end of the new pipeline to an end of the existing pipeline; and inserting cables into the connected new and existing pipelines.