PURPOSE: To securely cap against even a relatively dense case body and the cap, by providing a pair of right and left induction guides supporting the inner periphery of the opening of the cap body in the state that the opening of the cap body is positioned downward and a lifter forcing the case body on a transfer device to pass through between the induction guides of the pair of right and left guides.

CONSTITUTION: An induction guide 18 is fitted so that appropriate number of plate springs 20 are contracted as they go up at the four peripheral sides of a frame body having a larger dimension than the outer periphery of a vacant case 12. When the vacant case 12 is moved up from the lower side of the frame body 23 of the induction guide 18 by the lifter 22 for the vacant case, since the opening of cap body 7 is supported by the plate springs 20 at the four peripheral sides, the four peripheral walls of the cap body 7 is widened so as to expand the plate spring 20 and the vacant case 12 is closed with cap body 7. As a result, the cap body can be fitted in a small space on treating a case with cap and the cap hardly runs on to the case even if the cap body is deformed a little.