To provide a method of drilling a hard structure with a diamond core bit which prevents the occurrence of the accidents such as an electrical leakage or an electrical power failure due to the leakage of an aqueous solution by feeding a small amount of aqueous solution to the diamond core bit side, and improves cutting ability by reducing friction heat in cutting, and an aqueous solution supply device used for the same.

The small amount of oozed-out aqueous solution 14 is supplied on the outer surface of the diamond core bit 2. This small amount of aqueous solution is supplied to the diamond core bit 2 through an aqueous solution tank and a perforated sponge adjacent thereto or an oozing-out feeding member 9 or the like interposed therebetween. The electrical leakage or the electrical power failure due to water leakage or the like is prevented by the small amount of aqueous solution 14. Meanwhile, efficient drilling hole due to the reduction of friction heat can be performed.