PURPOSE: To form a protective film having superior corrosion and wear resistances on the inside of a pipe by cleaning the inside of the pipe, forming the layer of powder of a substance for coating, and irradiating a laser beam on the powder layer to melt the layer.

CONSTITUTION: The inside 1 of the pipe is cleaned, a slurry consisting of powder of the substance for coating and a liq. medium is applied to the inside 1 of the pipe, and the liq. medium is removed form a powder layer 2 on the inside 1 of the pipe. A laser beam L is successively irradiated on the powder layer 2 to melt the layer 2. By this melting, a coating layer 6 is formed.