Abstract: A coupling device for establishing a detachable connection for a tube system is to be improved so that while simple detachability of the pipe socket and tube is guaranteed, the pulling-off force is equivalent to firm clamping. To accomplish the task, a sleeve-like coupling box 7 is provided, which surrounds the tube 5 in a clamp-like manner and, for fixation on the pipe socket 2, it has, on the inside, a circumferential notch 8, into which two oppositely arranged projecting parts 4 of the pipe socket 2 snap. The coupling box 7 expands under the effect of a force acting laterally, so that the projecting parts 4 will disengage from the notch 8.