A connector assembly that includes a first connector and a second connector which are configured to mate with each other, wherein the first connector includes: a housing that has a first receiving space to receive the second connector, a slider that forms in the first receiving space a second receiving space to receive the second connector, is held by the housing such that the slider is slidable in a direction intersecting a mating direction, slides in a first direction to cause the second connector to move in the mating direction in which the first connector is mated to the second connector, and slides in a second direction opposite to the first direction to cause the second connector to move in a direction opposite to the mating direction, wherein the connector assembly includes, on an inner wall of the slider and an outer wall of the second connector, backlash restraining configurations (25, 53) that abut against each other at the time of mating completion to restrain backlash between the first connector and the second connector, characterised in that the backlash restraining configurations include: a first protrusion that is provided on the inner wall of the slider so as to protrude in an inside of the second receiving space, and a second protrusion that is provided on the outer wall of the second connector so as to protrude outward, and, at the time of mating completion, presses the first protrusion in a direction to expand the second receiving space so as to cause the slider to abut against an inner wall of the housing. a housing that has a first receiving space to receive the second connector, a slider that forms in the first receiving space a second receiving space to receive the second connector, is held by the housing such that the slider is slidable in a direction intersecting a mating direction, slides in a first direction to cause the second connector to move in the mating direction in which the first connector is mated to the second connector, and slides in a second direction opposite to the first direction to cause the second connector to move in a direction opposite to the mating direction, wherein the connector assembly includes, on an inner wall of the slider and an outer wall of the second connector, backlash restraining configurations (25, 53) that abut against each other at the time of mating completion to restrain backlash between the first connector and the second connector, characterised in that the backlash restraining configurations include: a first protrusion that is provided on the inner wall of the slider so as to protrude in an inside of the second receiving space, and a second protrusion that is provided on the outer wall of the second connector so as to protrude outward, and, at the time of mating completion, presses the first protrusion in a direction to expand the second receiving space so as to cause the slider to abut against an inner wall of the housing. a first protrusion that is provided on the inner wall of the slider so as to protrude in an inside of the second receiving space, and a second protrusion that is provided on the outer wall of the second connector so as to protrude outward, and, at the time of mating completion, presses the first protrusion in a direction to expand the second receiving space so as to cause the slider to abut against an inner wall of the housing.