PURPOSE: To test the airtightness of a container handily and easily, by injecting an alcohol solution with methylene blue or other pigment into a container to test the airtightness thereof depending on the presence of leakage of the solution and the degree thereof.

CONSTITUTION: Alcohol, especially, ethylalcohol is used as substance hydrophilic and excellent in the permeability into a finely leaked part. A coloring substance, preferably, a small amount of methylene blue is melted. Then, the solution thus obtained is poured into a container intended to check for airtightness. The container is allowed to stand for a while. Then, by examining the seepage of color from the container to detect the leakage tendency of the container.