PURPOSE: To prevent mixing of impurities into cooling medium, or formation of a shortcircuit by supplying specified film forming material into a passage for the cooling medium, and attaching the film forming material to an inner surface of the passage for forming a film of excellent durability.

CONSTITUTION: A glass film 90 is formed on the inner side of cooling holes 22a-22d as passages for cooling medium in a cell 20, and the film 90 is formed continuous without seam at matching parts of the cell 20 with a cooling member 30. The film 90 is also formed on the inner side of the passage for the cooling medium formed of the member 30 and the cell 20. Contact of the members such as the cell 20 and the member 30 for forming the passages for the cooling medium with the coiling medium can thus be prevented completely, so inconvenience such as mixing of impurities into the cooling medium can be prevented. By using the film 90 having electric insulation effect, formation of a shortcircuit between the members 30 can be eliminated, inconvenience such as electrolysis of the cooling medium by the film 90 can be prevented, and durability of a cell can be improved.