To provide a double pipe arrangement system by which cutting and back-filling workloads can be reduced and besides newly-laying pipe arrangement is easily possible inside the existing pipe arrangement even in the case where there are abrupt bent portions and branches in the existing pipe arrangement.

In a position biased to a pipe-axis direction of a peripheral wall of the existing pipe arrangement, at least two pipe inserting holes are bored. A flexible pipe whose diameter is smaller than those of the existing pipes making up part of the newly-laying pipes passes from one pipe inserting hole through the existing pipe to be laid so as to protrude outside the existing pipe via the other pipe inserting hole.