PURPOSE: To fit two members to each other without difficulty by getting a tubular male member butting against a female member made of flexible elastic material, then fitting them to each other as pressurized gas is forcibly inserted into a fitting recess of the female member from the inside of the male member.

CONSTITUTION: At the center of a flexible rubber female member 1 is formed a fitting recess 2 with the same shape as the fitting head 7 of a male member 5 through a narrow insertion opening 3. A conduction passage 6 is formed within the male member 5. Pressurized gas is then inserted into the conduction passage 6 while the fitting head 7 is abutting against the insertion opening 3, for pressing the male member 5. Thus two members 1, 5 can be easily and unforcedly fit to each other.