An electrical connection box comprising: a casing having a housing space inside for housing an electronic component; and a cover member that includes a wiring member holding part for holding a wiring member electrically connected to the electronic component, the cover member being fitted to the casing by being moved to a fitting direction with respect to the casing, wherein the cover member includes: a cover-member main body; at least one locking piece extended from the cover-member main body toward the fitting direction; a restriction piece that is extended from the cover-member main body toward the fitting direction, and is arranged along the locking piece in an arrangement direction orthogonal to the fitting direction; a plate part located in a midway of the fitting direction of the cover-member main body; and a rigid part that projects from the plate part toward the fitting direction, is disposed with a space provided with respect to the cover-member main body in an orthogonal direction orthogonal to each of the fitting direction and the arrangement direction, and is extended in the orthogonal direction, the casing includes: an insertion hole to which the wiring member is inserted; a locking reception part to which the locking piece is inserted; a pair of restriction reception parts (70a, 70b) that oppose to respective ends in the arrangement direction of a pair of the restriction pieces in a state in which the cover member is fitted to the casing; and a rigid reception part having a rigid-reception-part projecting wall part located between the rigid part and the cover-member main body in a state in which the rigid part is inserted and projects from the casing toward an opposite direction of the fitting direction, and the cover member is fitted to the casing. a casing having a housing space inside for housing an electronic component; and a cover member that includes a wiring member holding part for holding a wiring member electrically connected to the electronic component, the cover member being fitted to the casing by being moved to a fitting direction with respect to the casing, wherein the cover member includes: a cover-member main body; at least one locking piece extended from the cover-member main body toward the fitting direction; a restriction piece that is extended from the cover-member main body toward the fitting direction, and is arranged along the locking piece in an arrangement direction orthogonal to the fitting direction; a plate part located in a midway of the fitting direction of the cover-member main body; and a rigid part that projects from the plate part toward the fitting direction, is disposed with a space provided with respect to the cover-member main body in an orthogonal direction orthogonal to each of the fitting direction and the arrangement direction, and is extended in the orthogonal direction, a cover-member main body; at least one locking piece extended from the cover-member main body toward the fitting direction; a restriction piece that is extended from the cover-member main body toward the fitting direction, and is arranged along the locking piece in an arrangement direction orthogonal to the fitting direction; a plate part located in a midway of the fitting direction of the cover-member main body; and a rigid part that projects from the plate part toward the fitting direction, is disposed with a space provided with respect to the cover-member main body in an orthogonal direction orthogonal to each of the fitting direction and the arrangement direction, and is extended in the orthogonal direction, the casing includes: an insertion hole to which the wiring member is inserted; a locking reception part to which the locking piece is inserted; a pair of restriction reception parts (70a, 70b) that oppose to respective ends in the arrangement direction of a pair of the restriction pieces in a state in which the cover member is fitted to the casing; and a rigid reception part having a rigid-reception-part projecting wall part located between the rigid part and the cover-member main body in a state in which the rigid part is inserted and projects from the casing toward an opposite direction of the fitting direction, and the cover member is fitted to the casing. an insertion hole to which the wiring member is inserted; a locking reception part to which the locking piece is inserted; a pair of restriction reception parts (70a, 70b) that oppose to respective ends in the arrangement direction of a pair of the restriction pieces in a state in which the cover member is fitted to the casing; and a rigid reception part having a rigid-reception-part projecting wall part located between the rigid part and the cover-member main body in a state in which the rigid part is inserted and projects from the casing toward an opposite direction of the fitting direction, and the cover member is fitted to the casing.