A female housing of the female connector has a slider slidably installed in a direction orthogonal to a longitudinal joining direction. The slider includes a first cam provided with a first ridge portion, and a pair of opposing first and second slanting portions extending from the first ridge portion. The male housing of the male connector is formed with a second cam on an outer wall surface thereof. The second cam provided with a second ridge portion, a third slanting portion coming into abutment and slidably contacting with the first slanting portion of the slider, and a fourth slanting portion being slidably in contact with the second slanting portion and pressed and retained by the second slanting portion. Thus a half-fitted state can be detected and the connectors are prevented from loosening.