A battery accommodation casing includes a casing member having an approximate flat shape to house a laminate-sheathed cell therein in a sealing manner, a recess having a hollow shape in cross section and formed on a surface of the casing member, and a gas release mechanism located on a wall of the recess and releasing gas to outside, the gas being emitted from the laminate-sheathed cell within the casing member in an abnormal situation. Therefore, even where the casing member itself is somewhat deformed by the gas, the gas release mechanism can release the gas to outside, thus improving reliability in an abnormal situation.