Coupling device (10, 110) for fluid lines, comprising a receiving unit (12, 112) and a plug-in unit (14, 114), wherein the receiving unit (12, 112) is designed to be connected at a first end to a fluid line not belonging to the receiving unit (12, 112), and which defines a fluid flow channel in its interior, wherein the receiving unit (12, 112) comprises a closure element (34, 134) which, in a closed position, is designed to fluidically seal the fluid flow channel of the receiving unit (12, 112) between the first end and a second end of the receiving unit (12, 112) opposite the first end with respect to a main flow direction along the fluid flow channel, wherein the closure element (34, 134) is displaceable between the closed position and a release position, wherein the closure element (34, 134) is preloaded into the closed position using a spring element, wherein the closure element (34, 134) comprises a substantially cylindrical section (36, 136) which is formed free of perforations, wherein the entire spring element, in the release position of the closure element (34, 134), is arranged within a region which, along its entire longitudinal extent, viewed in a radial direction of the cylindrical section (36, 136), is completely overlapped by the cylindrical section (36, 136), wherein the closure element (34, 134) further comprises a partial section provided with perforations (38, 138), wherein the perforations (38, 138) of the partial section are designed as window-like openings (38, 138) which fluidically connect an interior of the closure element (34, 134) to an exterior of the closure element (34, 134), wherein the plug-in unit (14, 114) is designed to be connected at a first end to a further fluid line not belonging to the plug-in unit (14, 114), and which defines a fluid flow channel in its interior, wherein the plug-in unit (14, 114) has a contact surface (74, 82; 153, 182) which is designed to come into contact with a corresponding counter-contact surface (72, 32; 151, 132) of the closure element (34, 134) of the receiving unit (12, 112) so that, as the plug-in unit (14, 114) is progressively inserted into the receiving unit (12, 112), the closure element (34, 134) of the receiving unit is displaced from its closed position in the direction of the release position, wherein a sealing device is arranged on the receiving unit (12, 112) and/or on the plug-in unit (14, 114), said sealing device being designed to act between the receiving unit (12, 112) and the plug-in unit (14, 114) in such a way that the fluid flow channel of the receiving unit (12, 112) and/or the plug-in unit (14, 114) is fluidically sealed to an outside of the coupling device (10, 110), wherein the sealing device is arranged such that a fluidic seal is established between the receiving unit (12, 112) and the plug-in unit (14, 114) before the contact surface (74, 82; 153, 182) of the plug-in unit (14, 114) comes into contact with the counter-contact surface (72, 32; 151, 132) of the closure element, wherein the closure element of the receiving unit has a central bolt which has a free end that extends in the direction of the second end of the receiving unit and which is designed, on insertion of the plug-in unit into the receiving unit, in particular with its free end, to bear against a bolt-receiving surface formed on the closure element of the plug-in unit, so that on progressively inserting the plug-in unit into the receiving unit, wherein the plug-in unit (14, 114) also comprises a closure element (54, 154), the closure element of the plug-in unit or the closure element of the receiving unit is displaced from its closed position toward the release position, characterised in that the counter-contact surface (32; 132) of the closure element (34, 134) of the receiving unit (12, 112) is designed as a collar (32, 132) projecting radially from the closure element of the receiving unit (12, 112). wherein the closure element of the receiving unit has a central bolt which has a free end that extends in the direction of the second end of the receiving unit and which is designed, on insertion of the plug-in unit into the receiving unit, in particular with its free end, to bear against a bolt-receiving surface formed on the closure element of the plug-in unit, so that on progressively inserting the plug-in unit into the receiving unit, wherein the plug-in unit (14, 114) also comprises a closure element (54, 154), the closure element of the plug-in unit or the closure element of the receiving unit is displaced from its closed position toward the release position, characterised in that the counter-contact surface (32; 132) of the closure element (34, 134) of the receiving unit (12, 112) is designed as a collar (32, 132) projecting radially from the closure element of the receiving unit (12, 112).