Abstract: The purpose of the present invention is to provide a lathe positioning apparatus such that a work held by a chuck can be positioned at an arbitrary position in main shaft direction and the installation space and the size of the apparatus can be decreased. A lathe positioning apparatus for positioning a work W held by a chuck 6 in a main shaft 4 direction is provided with an apparatus body 12 having a shaft center along the main shaft 4 direction. An abutting portion 26 for abutting the work W is formed on a chuck 6 side end of the apparatus body 12. A mechanism for advancing or withdrawing the abutting portion 26 with respect to the chuck 6 is provided. An extension/contraction mechanism for extending or contracting the apparatus body 12 in the main shaft 4 direction is provided in the apparatus body 12. The abutting portion 26 is advanced or withdrawing with respect to the chuck 6 by the extending or contracting by the extension/contraction mechanism.