To solve the problem that, when it is intended to collect a core with a known bearing during a soil investigation boring, a twist in a non-rotary rod as accumulation of machining errors in members and co-rotation with a rotating boring rod results in an error in the bearing of the collected core.

A double-pipe device is configured of: a rotating outer pipe ; and an inner pipe which is placed coaxially and in a free-rotating position inside the outer pipe. The inner pipe has a continuous rotation-producing system that converts the axial-flow fluid motion of a fluid passing inside the outer pipe or the inner pipe to a rotary motion in an reverse rotation to the rotary direction of the outer pipe, so that a twist in the inner pipe due to machining errors in members and co-rotation with the rotating outer pipe can be reduced.