To provide a core sampling technique capable of shortening the time required for sampling a geological core and capable of surely sampling the core under an accurate state.

A core sampler 1 has a cylindrical casing 2 having an excavating means 2c at the periphery 2b of a front-end opening section 2a, a cylindrical excavating tube 3 being inserted into the casing 2 and having a cutting means 3c at the periphery 3b of a front-end opening section 3a, a core housing means 5 installed in the tube 3 for housing the geological core 4 taken into the tube 3 from the opening section 3a of the tube 3, a water supply path 6 mounted on the tube 2 for supplying the front end section of the tube 3 with water, a connecting mechanism 7 connecting the tube 3 and the casing 2 in a manner that the tube 3 and the casing 2 can be engaged or disengaged and a cylindrical driving shaft 8 combining a fluid feeding means for feeding the path 6 with water from a ground.