BATTERY CASE AND SECONDARY BATTERY INCLUDING THE SAME

Provided is a technique improving assemblability when a sealing plate is attached to an opening of a case body. The battery case (41) disclosed herein includes: a case body (41a) in bottomed rectangular parallelepiped shape having a substantially rectangular opening (41a1); and a sealing plate (41b) attached to the opening (41a1). The opening (41a1) of the case body (41a) has long side portions (43a, 44a), short side portions (45a, 46a), R portions (47a - 47d), and steps (43a, 44a) protruding from the inner surfaces of the short side portions (45a, 46a). The R portions (47a - 47d) are each provided with a gradual change region (47c3) where a shape of each the steps (48a, 48b) changes to be gradually close to the shape of each of the inner surfaces of the long side portions (43a, 44a).