To provide a pressure tight case constructed by seaming between a flange of a case body and a lid, durability of the flange being improved.

The pressure tight case includes: an upward-opening bottomed-cylindrical-case body 1; and a lid 2 which is fixed to an opening at an upper part of the upward-opening bottomed-cylindrical-case body 1 by double seaming while being sealed with a first sealing agent 3 and a second sealing agent 4. The case body 1 is made of a PET and the lid 2 is made of aluminum. A metallic coating layer 9 is formed on an overlapping surface area of the flange 1f of the case body 1 with a surface of the lid 2. The first sealing agent 3 is applied to an under surface of an inner ring part 2b and the second sealing agent 4 is applied to an under surface of the flange 1f, and the double seaming is performed.