To provide a joint jig capable of preventing excessive time and efforts from being spent for aligning a flange joint.

A joint jig 1 for aligning a pair of abutted flange joints comprises: a base member 2 including a pair of counter parts 20, 21 which oppose each other while being spaced apart from each other, and a continuation part 22 continued to the counter parts 20, 21; an insertion member 4 which is provided in one of the counter parts 20, 21 and inserted to a through hole of at least one flange joint in the state where the pair of flange joints F, F are interposed between the pair of counter parts 20, 21; a pressing member 4 which is provided in the continuation part 22 and is movable across an inserting direction of the insertion member 4; and a holding part 5 for holding the pair of flange joints between the pair of counter parts 20, 21.