To provide a sampling device of high actuation reliability and excellent durability for geological survey by boring.

A device main body 1 is composed of a head cover 4, an outer cylinder 5, a center shaft 6, a guide block 7, a piston 8, a sampling cylinder 9 connected to the piston 8, and a clutch cylinder 10, a water passage 21 to introduce pressure water into a cylinder chamber 11 is provided, the clutch cylinder 10 has a pressure receiving part 12 facing the cylinder chamber 11 at an upper and, an upward tapered outer circumferential surface 14 is provided to face an upward tapered inner circumferential surface 13 on the side of the piston 8, a clutch ball 16 is engaged in a radial direction through hole 15 facing the tapered outer circumferential surface 14, it is energized upward by a spring 17, and the clutch ball 16 is normally pressed to get in contact with an outer circumferential surface of the center shaft 6 and the tapered inner circumferential surface 13 of the piston 8 to lock the piston 9 to the center shaft 6, while, as pressure water is supplied to the cylinder chamber 11, the clutch cylinder 10 is pushed down to release locking, and the piston 8 is lowered to let the sampling cylinder 9 enter into the ground E.