A casing for an electrical apparatus that houses the electrical apparatus, the casing comprising: a casing body having an opening; a cover body that includes a flat plate-like cover portion having a rectangular shape and a curved cover portion (24, 25) continuous to one side (21a, 21b) of the flat plate-like cover portion and is attached to the casing body to cover the opening; a sealing member (5, 6) that is arranged between the casing body and the flat plate-like cover portion and seals between the casing body and the flat plate-like cover portion, and a communication portion that is provided inside the curved cover portion (24, 25) in a manner extending along the one side (21a, 21b) of the flat plate-like cover portion and communicates with outside between the curved cover portion (24, 25) and the casing body, wherein the casing body has a box shape including: a first wall having a rectangular shape; a second wall continuous to a first side of the first wall; a third wall that opposes the second wall and is continuous to a second side of the first wall; a fourth wall continuous to a third side of the first wall, the second wall, and the third wall; a fifth wall that opposes the fourth wall and is continuous to a fourth side of the first wall, the second wall, and the third wall, and the sealing member (5, 6) is arranged in a manner extending parallel to the one side between an end surface of the fourth wall facing opposite from the first wall and the flat plate-like cover portion, the curved cover portion (24, 25) is curved from the one side of the flat plate-like cover portion toward the first wall, and the casing further comprises a partition wall (30, 31) for separating the communication portion from an inside of the casing body, characterized in that the first wall, the second wall, the third wall, the fourth wall and fifth wall are integrally provided, and a flange portion (14d, 15c) having an arcuate outer peripheral surface is integrally provided between the end surface of the fourth wall and the third wall, and a gap is provided between the outer peripheral surface of the flange portion (14d, 15C) and an inner peripheral surface of the curved cover portion (24, 25). a casing body having an opening; a cover body that includes a flat plate-like cover portion having a rectangular shape and a curved cover portion (24, 25) continuous to one side (21a, 21b) of the flat plate-like cover portion and is attached to the casing body to cover the opening; a sealing member (5, 6) that is arranged between the casing body and the flat plate-like cover portion and seals between the casing body and the flat plate-like cover portion, and a communication portion that is provided inside the curved cover portion (24, 25) in a manner extending along the one side (21a, 21b) of the flat plate-like cover portion and communicates with outside between the curved cover portion (24, 25) and the casing body, wherein the casing body has a box shape including: a first wall having a rectangular shape; a second wall continuous to a first side of the first wall; a third wall that opposes the second wall and is continuous to a second side of the first wall; a fourth wall continuous to a third side of the first wall, the second wall, and the third wall; a fifth wall that opposes the fourth wall and is continuous to a fourth side of the first wall, the second wall, and the third wall, and a first wall having a rectangular shape; a second wall continuous to a first side of the first wall; a third wall that opposes the second wall and is continuous to a second side of the first wall; a fourth wall continuous to a third side of the first wall, the second wall, and the third wall; a fifth wall that opposes the fourth wall and is continuous to a fourth side of the first wall, the second wall, and the third wall, and the sealing member (5, 6) is arranged in a manner extending parallel to the one side between an end surface of the fourth wall facing opposite from the first wall and the flat plate-like cover portion, the curved cover portion (24, 25) is curved from the one side of the flat plate-like cover portion toward the first wall, and the casing further comprises a partition wall (30, 31) for separating the communication portion from an inside of the casing body, characterized in that the first wall, the second wall, the third wall, the fourth wall and fifth wall are integrally provided, and a flange portion (14d, 15c) having an arcuate outer peripheral surface is integrally provided between the end surface of the fourth wall and the third wall, and a gap is provided between the outer peripheral surface of the flange portion (14d, 15C) and an inner peripheral surface of the curved cover portion (24, 25).