To provide a positioning tool for facilitating the positioning of a work on the upper surface of a work support table.

An engagement recess part 14c is formed in the lower end face of a position regulating member 14 and a position regulating key 15 is detachably fitted in the engagement recess part 14c. The cylindrical part 15b of the position regulating key 15 is fitted in a guide groove 13a of a fitting groove 13 formed in the work support table 12. A male screw 16a of a movable fitting member 16 is threaded with a screw hole 14a formed in the position regulating member 14. A fastening bolt 17 penetrates through a through hole 15d of the position regulating key 15, an insertion hole 14b of the position regulating member 14, and a through hole 16b of the movable fitting member 16 with its top facing upward, a nut 18 is threaded with its upper part, and the position regulating member 14 and the movable fitting member 16 are fastened and fixed to the upper surface of the work support table 12. The side of the work W is made to abut on and positioned in the work position regulating plane 14d formed in the outer circumferential surface of the position regulating member 14.