PURPOSE: To cover the inner circumference of a drilled hole simply and safely by a method wherein an air motor for driving a turning rotor is provided, and an ejection nozzle provided to the front end of a liquid feed pipe for supplying acid-resistant covering material is made to face the inside of the turning rotor.

CONSTITUTION: A rope is attached to a hook 8 on the tail end of a covering apparatus main body 1, and the main body 1 is moved to the bottom of a drilled hole 11. Then, liquid acid-resistant covering material is supplied through a liquid feed pipe 4 and ejected from an ejection nozzle 5 and at the same time, an air motor 6 is driven with compressed air sent through an air pipe 7 and thereby a turning rotor 3 is turned. Then, the acid-resistant covering material is sprayed by centrifugal force produced by the rotor 3 through pores 2 provided to the periphery of the rotor 3, and an acid- resistant covering part 16 is formed with the main body 1 moved slowly toward the upper side. Thereby, the inside of the drilled hole 11 can be covered simply and safely as there is no need of fearing electric leakage because of using the air motor 6 while high air pressure is obviated because of utilizing the centrifugal force produced by the turning rotor 3.