PURPOSE: To prevent failure of insertion due to any obstacles in the way be a method wherein in the case that a bung hole bung is inserted into a bung mounting hole provided in a container body from inside of the container body, the bung is guided by a ball-shaped part of a cap surface.

CONSTITUTION: A bung hole bung 1 consists of a bung body 13 which is formed of a bung cylinder 11 and a flange 12, and a cap 14, and a surface part of the cap 14 is formed entirely in a ball surface. The bung hole bung 1 is taken out from a receiving part 33 by suction and fixing by a vacuum suction part 41. In addition, the bung hole bung 1 and the vacuum suction part 41 are rotated around a rotary shaft 42, the cap 14 is inserted into a bung mounting hole 21 of a container body 2 from inside of the container body 2, and the flange is brought into contact with an inner surface of the container body 2. In this state, the vacuum sunction part 41 is stopped rotating and a grooved block 8 is made to go down into contact with the container body 2. Further, if an ultrasonic horn 6 is brought into contact with an outer surface of the container body 2 with which the flange is contacted and oscillates ultrasonic waves, the inner surface of the container body 2 and the flange 12 are sealed by friction heat generated on the contact surface.