Abstract: A module is placed inside a chamber that can be sealed hermetically. The module includes a substrate incorporating a plurality of electronic circuit parts, a frame connected to the substrate so as to enclose the plurality of electronic circuit parts, and a cover placed facing the substrate and connected to the frame so as to cover an opening portion of the frame. The pressure in the chamber is reduced to a first pressure P1, and then the pressure is increased from the first pressure P1 to a second pressure P2. A liquid is filled into the module through a hole formed in the cover within the chamber, and the pressure inside the chamber is increased from the second pressure P2 to a third pressure P3. Then, the hole of the cover in the chamber is closed to seal the module hermetically, thereby sealing the liquid in the module. Thereafter, the pressure in the chamber is increased from the third pressure P3 to an atmospheric pressure P0, and the module is taken out of the chamber.