To speedily and accurately set a facing distance between an upper jaw and a lower jaw to a facing distance consistent with a nut, by providing a position displaying the facing distance between the upper jaw and the lower jaw with a bolt diameter indicating division for indicating the bolt diameter of a bolt screwed with a nut consistent with given facing distance.

A facing distance indicating division for indicating moving position of a lower jaw 2 that approaches or separates from an upper jaw 1 is formed from a bolt diameter indicating division 5 for a bolt diameter L2 of a bolt 4 screwed with a nut 3 whose nut diameter L1 is consistent with the facing distance between the upper jaw 1 and the lower jaw 2. When the lower jaw 2 is approached or separated from the upper jaw 1, the moving position indicated by movement of the lower jaw 2 indicates the bolt diameter L2 of the bolt 4 screwed with the nut 3. Therefore, only operation of an operation portion 6 can speedily and accurately set the facing distance between the upper jaw 1 and the lower jaw 2 to the distance consistent with the nut diameter L1 of the nut 3 screwed with the bolt 4.