An electrical connection box comprising: an insulating housing; a conductive relay bus bar held by the housing within the housing; an electronic component configured to be inserted to an accommodation completion position within the housing and provided with a conductive bus bar to be connected to the relay bus bar; and a fixing structure configured to physically and electrically connect the bus bar at the accommodation completion position to the relay bus bar held by the housing in advance, wherein the relay bus bar includes a plurality of electrical connection bodies and a coupling body coupling the electrical connection bodies, at least one of the electrical connection bodies is a plate-like flat electrical connection body, two flat surfaces (21a, 21b) of which extend along an insertion direction of the electronic component with respect to the housing within the housing, the bus bar includes a plate-like flat electrical connection body, two flat surfaces (41a, 41b) of which extend along the insertion direction, one of the two flat surfaces (21a, 21b) of the flat electrical connection body of the relay bus bar and one of the two flat surfaces (41a, 41b) of the flat electrical connection body of the bus bar are mating surfaces to be brought into contact with each other by the fixing structure, at least one of the respective flat electrical connection bodies (21A, 40) of the relay bus bar and the bus bar has such flexibility as to enable elastic deformation in a direction crossing the mating surfaces (21a, 41a), applying a reaction force accompanying the elastic deformation to the other flat electrical connection body, to which the one flat electrical connection body is to be connected, in a state in which the flat electrical connection body of the bus bar at the accommodation completion position has not been connected to the flat electrical connection body of the relay bus bar by the fixing structure, and the housing includes a receiving portion configured to receive, from the electronic component, a force applied to the flat electrical connection body of the bus bar from the flat electrical connection body of the relay bus bar. an insulating housing; a conductive relay bus bar held by the housing within the housing; an electronic component configured to be inserted to an accommodation completion position within the housing and provided with a conductive bus bar to be connected to the relay bus bar; and a fixing structure configured to physically and electrically connect the bus bar at the accommodation completion position to the relay bus bar held by the housing in advance, wherein the relay bus bar includes a plurality of electrical connection bodies and a coupling body coupling the electrical connection bodies, at least one of the electrical connection bodies is a plate-like flat electrical connection body, two flat surfaces (21a, 21b) of which extend along an insertion direction of the electronic component with respect to the housing within the housing, the bus bar includes a plate-like flat electrical connection body, two flat surfaces (41a, 41b) of which extend along the insertion direction, one of the two flat surfaces (21a, 21b) of the flat electrical connection body of the relay bus bar and one of the two flat surfaces (41a, 41b) of the flat electrical connection body of the bus bar are mating surfaces to be brought into contact with each other by the fixing structure, at least one of the respective flat electrical connection bodies (21A, 40) of the relay bus bar and the bus bar has such flexibility as to enable elastic deformation in a direction crossing the mating surfaces (21a, 41a), applying a reaction force accompanying the elastic deformation to the other flat electrical connection body, to which the one flat electrical connection body is to be connected, in a state in which the flat electrical connection body of the bus bar at the accommodation completion position has not been connected to the flat electrical connection body of the relay bus bar by the fixing structure, and the housing includes a receiving portion configured to receive, from the electronic component, a force applied to the flat electrical connection body of the bus bar from the flat electrical connection body of the relay bus bar.