To provide a device for sampling an underground specimen, which is provided at an expansion head with a diameter-enlargement blade, capable of sampling an uncured underground specimen immediately after filling of an enlarged base bulb with base hardening liquid in a state that the diameter-enlargement blade is contracted, such that the sampled underground specimen can be collected without mixture of other filling; and a method for sampling an underground specimen.

A sampling device includes an outer pipe and an inner pipe which is housed inside the outer pipe and provided with a window hole for sampling an underground specimen. A hydraulic cylinder mechanism, which is a separate and independent mechanism from an opening/closing mechanism of a diameter-enlargement blade, is arranged in parallel with the sampling device composed of the outer and inner pipes. The inner pipe is retractable from the outer pipe, interlocking with the expansion and contraction of the hydraulic cylinder mechanism. The window hole is also retractable from the outer pipe in connection with the retractable movement.