| 摘要 |
PROBLEM TO BE SOLVED: To protect a filter against damage caused by contact with an external object and to prevent a hermetically closed vessel from degrading waterproofness by a method wherein the filter is fixed to the inner wall of the hermetically closed vessel, and vent holes are provided in the inner wall so as not to enable the filter to be visually observed. SOLUTION: A vent hole 4A composed of a first vent hole 8 and a second vent hole 10 is provided to enable the inside and outside of a hermetically closed vessel to communicate with each other. The first vent hole 8 is provided like an L shape inside an outer case 1 which forms the hermetically closed vessel together with a shielding member 9a. The inner side edge 8A of the first vent hole 8 is covered with a filter 5 which is high in water resistance and air permeability. The outer side edge 8B of the first vent hole 8 is firmly fixed to the outer wall of the outer case 1, by which the outer side edge 8B is covered with the shielding member 9. The shielding member 9 is equipped with the second vent hole 10 which is provided so as to confront the outer side edge 8B of the first vent hole 8 but not to confront the inner side edge 8A.
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