A lock arm includes a pair of guide rails protruding toward side walls, extending in a detachment direction, and formed to have a part on the detachment direction side facing a direction away from a main body. A detection member includes a rib positioned on the detachment direction side of an abutment surface and positioned to be sandwiched between the main body and a locking protrusion, and is relatively movable with respect to a housing between a fixing position and the main locking position, the fixing position at which a distal end of a detection arm opposes a locking portion in the engagement direction, the locking protrusion is sandwiched between the rib and the main body while opposing the abutment surface in an insertion and removal direction, and a protruding body is positioned to oppose the part of the guide rail on the detachment direction side.