PROBLEM TO BE SOLVED: To provide a casing boring method suitable for investigating/observing a ground weak in independence, and to provide its expensive device for executing the same. SOLUTION: The casing boring device suitable for investigating/observing the ground 1 weak in independence such as a sand ground or a soft clay ground comprises a weight of a loading means 20 for statically putting a transparent casing 5 of a transparent acrylic resin through the ground 1 and a load eliminating means 30 for evacuating drill debris. The transparent casing 5 is a regular hexagonal polyhedron cylinder body and an extension frame 6 is added thereto as required. After the transparent casing 5 is statically put through the ground, image pickup equipment 40 is inserted into the transparent casing 5 for picking up the images of a borehole wall face. The picked-up images are used for investigating/observing the ground. COPYRIGHT: (C)2006,JPO&NCIPI