To provide a wood joining jig and a bolt having a locking piece which are easy in performing the fitting work and the additional tightening, and dispense with carving.

A wood joining jig is provided with a bolt 12 having a first locking piece and a nut 51 to fix a pulling metal fitting to be arranged at a corner of a cross part of a wooden member and beams 2, 3 to the beam 2, and a bolt 13 having a second locking piece and a nut 52 to pull and fix the pulling metal fitting 11 to the beam 3 side. The bolt 12 having the first locking piece and the bolt 13 having the second locking piece are provided with bolt parts 31, 32 to pierce the beams 2, 3 and the pulling metal fitting 11 and a flat plate shaped head part 34 to be locked flush to the surface of the beam, and locking pieces 35, 36 which bite the beams 2, 3 and lock them when the nuts 51, 52 are tightened to the bolt parts 31, 32 with not less than the prescribed torque are provided on an outer circumference of the bolt parts 31,32.