A release auxiliary device (6) includes a base part (51) that is provided fixedly with respect to a receptacle (11), and an auxiliary lever (52) that is provided elastically deformable with respect to the base part (51) and elastically deformable in an orthogonal direction with respect to a direction in which a lever (41) is deformed. The auxiliary lever (52) includes an inclined pressing part (62) that is touchable, from a side, to an end portion of the lever (41), the inclined pressing part (62) presses against the end portion of the lever (41) and moves the lever (41) by pressing an outer surface side of the auxiliary lever (52) and deforming the auxiliary lever (52), enabling release of the engagement between engaging portions (42, 28).