An apparatus for inserting an elongated device into a body cavity has a valve having a longitudinal axis. The valve is provided with a housing having a cup-shaped recess and a base, a first channel section provided in said base, a plunger having an end face, said plunger being at least with its end face inserted into and displacable within the cup-shaped recess, a second channel section provided in the plunger, and a hollow cylindrical elastic seal arranged within the cup-shaped recess between said base and said end face, said seal having an outer face and an inner face defining there between a cross section of the seal, a third channel section provided in the seal and surrounded by the inner face. The third channel section forms together with the first channel section and the second channel section a central channel, said central channel extending and being continuous along said longitudinal axis. Said seal is provided with a change in said cross section in a region along said longitudinal axis.
