A housing assembly comprising an insulating first housing and an insulating second housing of a pair of electric connectors to be coupled or uncoupled, and a reinforcing member for enhancing the coupling strength of these housings,, wherein with reference to a depth direction, a width direction and a height direction all being perpendicular to each other, the second housing is provided with a cavity, which opens on a front side in the depth direction and into which the first housing is to be fitted, the first housing is provided with a lock arm, which extends from a rear side to a front side in the depth direction and can be flexed to a lower side and is provided with a lock pawl on a higher side thereof, of walls facing the cavity in the second housing, a wall on a higher side in relation to the cavity is provided with a fitting part, which fits with the lock pawl when the lock arm shifts rearward and only after the lock pawl gets over the fitting part through flexure of the lock arm, the first housing is provided with a receiving chamber, which penetrates into the first housing in the depth direction, the reinforcing member having a body is inserted into the receiving chamber such that the reinforcing member can be slid between a front side position wherein the body is on the front side of the first housing and a rear side position being displaced rearwardly from the front side position, inside the receiving chamber of the first housing, first protruding parts are fixed on the first housing and protrude laterally outwardly to both sides in the width direction, inside the cavity of the second housing, second protruding parts are fixed on the second housing and protrude laterally outwardly to both sides in the width direction, the reinforcing member is provided with a pair of flexible fitting arms, which are adapted to flex laterally in the width direction, and which extend rearward from the body and are spaced apart in the width direction and are substantially parallel to each other, each one of the fitting arms is respectively provided with a top-end-side concaved part, which concaves from an inner side toward an outer side in the width direction and is to fit with a respective one of the first protruding parts when the reinforcing member is at the front side position, and each one of the fitting arms is respectively further provided with a root-end-side concaved part, which concaves from the inner side toward the outer side in the width direction at a location forward from the top-end-side concaved part in the depth direction and which is to fit with a respective one of the first protruding parts and a respective one of the second protruding parts when the first housing fits in the cavity of the second housing and the reinforcing member is at the rear side position, and the housing assembly being so structured that when the reinforcing member is held at the front side position by fitting the top-end-side concaved parts and the first protruding parts together, then the first housing is inserted into the cavity of the second housing, and the reinforcing member or the first housing is pushed rearward toward the second housing, the lock arm is flexed and brought into a position in which the lock arm will interfere with the reinforcing member to prevent the reinforcing member from sliding rearward into the first housing, and the fitting arms will be pushed by the second protruding parts to move apart from one another laterally outwardly to both sides in the width direction and thereby release the top-end-side concaved parts from the first protruding parts, and when the first housing is fitted in the cavity of the second housing, the lock arm will be at least partially restored by unflexing due to fitting of the lock pawl with the fitting part, allowing the reinforcing member to slide rearward into the first housing, and when the reinforcing member is pushed to the rear side position in relation to the first housing, the root-end-side concaved parts will receive and fit with both the first protruding parts as well as the second protruding parts.