A locating apparatus for a machine tool comprising: - a supporting portion suitable to be placed at a fixed point on a machining surface of an object, - detection means comprising a first cable or a second cable designed to connect said locating apparatus with said machine tool, and - a locating portion configured to release or receive said cable (70, 71) in such a way as to measure the distance (L1, L2) detected between said machine tool and said locating apparatus and including at least one frame, a first device, a second device and a third device, - said first device being attached to said frame and suitable for receiving or releasing said cable (70, 71) in opposition to or pushed by an elastic element, - said second device being attached to said frame and comprising a transmission member designed to allow the passage of said cable (70, 71) from said first device to said third device (80, 82), - said third device being attached to said frame and suitable for allowing the release or reception of said cable (70, 71) by said locating apparatus towards said machine tool and said apparatus being characterised in that - said first device comprises a discoidal element rotating around an axis of rotation with respect to said frame in such a way as to wind or release said cable (70, 71) on a winding surface extending around said axis of rotation and around which said cable (70, 71) is wound, - said second device includes at least one guiding slider suitable for conveying said cable (70,71) towards said third device along a conveying direction and configured to move, also moving said conveying direction, along a translation direction parallel to said axis of rotation in proportion to the rotation of said discoidal element, and in that - said third device includes a funnel-shaped slot at which is arranged a cable-guiding spinner to direct the exit of said detection means from said locating apparatus. - a supporting portion suitable to be placed at a fixed point on a machining surface of an object, - detection means comprising a first cable or a second cable designed to connect said locating apparatus with said machine tool, and - a locating portion configured to release or receive said cable (70, 71) in such a way as to measure the distance (L1, L2) detected between said machine tool and said locating apparatus and including at least one frame, a first device, a second device and a third device, - said first device being attached to said frame and suitable for receiving or releasing said cable (70, 71) in opposition to or pushed by an elastic element, - said second device being attached to said frame and comprising a transmission member designed to allow the passage of said cable (70, 71) from said first device to said third device (80, 82), - said third device being attached to said frame and suitable for allowing the release or reception of said cable (70, 71) by said locating apparatus towards said machine tool - said first device comprises a discoidal element rotating around an axis of rotation with respect to said frame in such a way as to wind or release said cable (70, 71) on a winding surface extending around said axis of rotation and around which said cable (70, 71) is wound, - said second device includes at least one guiding slider suitable for conveying said cable (70,71) towards said third device along a conveying direction and configured to move, also moving said conveying direction, along a translation direction parallel to said axis of rotation in proportion to the rotation of said discoidal element, - said third device includes a funnel-shaped slot at which is arranged a cable-guiding spinner to direct the exit of said detection means from said locating apparatus.