An electrical connection box comprising: a box main body including a cylindrical sidewall that surrounds a housing space for accommodating an electronic component, and a locking part disposed on an outer face of the sidewall; and a cover that is fitted to one end of the sidewall and closes an opening of the sidewall, wherein the sidewall includes a first wall part, and a second wall part opposite the first wall part in a first direction, the locking part includes a first locking part disposed on the first wall part, and a second locking part disposed on the second wall part, the cover includes a first opposing wall opposite the first wall part, a flexible first lock piece that is disposed on an outer face of the first opposing wall and locked by the first locking part, a second opposing wall opposite the second wall part, and a flexible second lock piece that is disposed on an outer face of the second opposing wall and locked by the second locking part, the first opposing wall includes a first opposing part, a second opposing part, and a connection part that connects the first opposing part and the second opposing part, the first opposing part and the second opposing part extend along a second direction that is orthogonal to the first direction, and also neighboring to each other in the second direction, the first lock piece is configured such that engagement with the first locking part is released by being pressed toward a side of the second opposing wall, and the second lock piece is configured such that engagement with the second locking part is released by being pressed toward a side of the first opposing wall, characterized in that the second opposing part is located closer to the second opposing wall side than the first opposing part is, the first lock piece is located at an end part of the first opposing part close to the second opposing part. a box main body including a cylindrical sidewall that surrounds a housing space for accommodating an electronic component, and a locking part disposed on an outer face of the sidewall; and a cover that is fitted to one end of the sidewall and closes an opening of the sidewall, wherein the sidewall includes a first wall part, and a second wall part opposite the first wall part in a first direction, the locking part includes a first locking part disposed on the first wall part, and a second locking part disposed on the second wall part, the cover includes a first opposing wall opposite the first wall part, a flexible first lock piece that is disposed on an outer face of the first opposing wall and locked by the first locking part, a second opposing wall opposite the second wall part, and a flexible second lock piece that is disposed on an outer face of the second opposing wall and locked by the second locking part, the first opposing wall includes a first opposing part, a second opposing part, and a connection part that connects the first opposing part and the second opposing part, the first opposing part and the second opposing part extend along a second direction that is orthogonal to the first direction, and also neighboring to each other in the second direction, the first lock piece is configured such that engagement with the first locking part is released by being pressed toward a side of the second opposing wall, and the second lock piece is configured such that engagement with the second locking part is released by being pressed toward a side of the first opposing wall, characterized in that the second opposing part is located closer to the second opposing wall side than the first opposing part is, the first lock piece is located at an end part of the first opposing part close to the second opposing part.