A connection device for connecting an end section of a tube comprises a tubular body defining a channel, a holding device for securing the tube end section within the channel in a sealed manner, and a bushing mounted in the channel to slide between a standby position in which the bushing is spaced apart from a stop at its recess within the channel and a recessed operating position in which the bushing presses against the stop. The bushing comprises, downstream from the holding device by reference to a direction of insertion of the end section of the tube into the body, at least one leg arranged to oppose the movement of the bushing toward the operating position and to be retracted by the end section of the tube when the bushing is engaged within the end section of the tube over a predetermined length.