The invention relates to a positioning mechanism (1) for releasably fixing at least one position of a positioning means (3) which can be displaced more or less linearly relative to positioning means (2) fixedly connected to a structure (45), e.g. a shoe, which provides a mount for at least one displaceable coupling means (9) which engages under the action of a spring system (39) in a female coupling part (20) of the positioning means (2) connected to the structure (45) in a position which fixes the position of the positioning means (2, 3) relative to one another. The coupling means (9) is mounted in the displaceable positioning means (3) so that it can be linearly displaced in a direction perpendicular to the displacement direction of the positioning means (3) and, in a position fixing the position between the positioning means (2, 3), engages by means of a coupling projection (21) with the female coupling part (20) of the positioning means (2) connected to the structure (45) and in a positioning seat (42) disposed in the displaceable positioning means (3).