A cover for covering a covered body, the covered body including a synthetic resin L-shaped unit body attachable to a corner portion formed by a first surface and a second surface of a battery, a first fixing portion of the unit body abutting on the first surface, and a second fixing portion of the unit body abutting on the second surface, the cover comprising: a top wall configured to cover the covered body, the top wall including a first top wall portion and a second top wall portion, a first side wall connected to one end of the second top wall portion; a second side wall connected to other end of the second top wall and facing the first side wall; and a lock releasing portion, wherein the first side wall comprises a locking portion engageable with a locked portion of the covered body, the second side wall comprises an opposed locking portion engageable with an opposed locked portion of the covered body, and the lock releasing portion comprises: a release operation portion inclined and projecting from a connected portion of the second top wall portion and the first side wall; and a connecting portion connecting the release operation portion with the first side wall around the locking portion, or the release operation portion with the locking portion, characterized by the first top wall portion being suitable for covering an upper surface of the first fixing portion, the second top wall portion being suitable for covering the second fixing portion, and the release operation portion being inclined and projecting from a connected portion of the second top wall portion and the first side wall in a cover mounting direction. the covered body including a synthetic resin L-shaped unit body attachable to a corner portion formed by a first surface and a second surface of a battery, a first fixing portion of the unit body abutting on the first surface, and a second fixing portion of the unit body abutting on the second surface, the cover comprising: a top wall configured to cover the covered body, the top wall including a first top wall portion and a second top wall portion, a first side wall connected to one end of the second top wall portion; a second side wall connected to other end of the second top wall and facing the first side wall; and a lock releasing portion, wherein the first side wall comprises a locking portion engageable with a locked portion of the covered body, the second side wall comprises an opposed locking portion engageable with an opposed locked portion of the covered body, and the lock releasing portion comprises: a release operation portion inclined and projecting from a connected portion of the second top wall portion and the first side wall; and a connecting portion connecting the release operation portion with the first side wall around the locking portion, or the release operation portion with the locking portion, characterized by the first top wall portion being suitable for covering an upper surface of the first fixing portion, the second top wall portion being suitable for covering the second fixing portion, and the release operation portion being inclined and projecting from a connected portion of the second top wall portion and the first side wall in a cover mounting direction. a top wall configured to cover the covered body, the top wall including a first top wall portion and a second top wall portion, a first side wall connected to one end of the second top wall portion; a second side wall connected to other end of the second top wall and facing the first side wall; and a lock releasing portion, wherein the first side wall comprises a locking portion engageable with a locked portion of the covered body, the second side wall comprises an opposed locking portion engageable with an opposed locked portion of the covered body, and the lock releasing portion comprises: a release operation portion inclined and projecting from a connected portion of the second top wall portion and the first side wall; and a connecting portion connecting the release operation portion with the first side wall around the locking portion, or the release operation portion with the locking portion, characterized by the first top wall portion being suitable for covering an upper surface of the first fixing portion, the second top wall portion being suitable for covering the second fixing portion, and the release operation portion being inclined and projecting from a connected portion of the second top wall portion and the first side wall in a cover mounting direction.