To easily confirm a fastening torque by safely constructing shape steel joining by fastening an opposite bolt of a channel joint fitting formed in C-shape in a heavy construction joint.

There is provided a joining confirmation method in a joint fitting which is formed by: screwing a bolt 4 toward an internal opposite surface of the other side through an internal opposite surface of one side from outside on one side of the internal opposite surface of a steel material insertion groove 2 formed on a joint body; providing a receiving implement 6 opposite to the bolt 4 on an inner opposite surface; protrusively disposing a male screw 9on a head part 8 of the bolt 4; and screwing a nut 4' to a male screw 9. Therein, a washer 10 having a bending part 10' is interposed between the nut 4' and the male screw 9, the nut 4' is screwed to the male screw 9 via the washer and, thereby, a steel material 11 inserted into the steel material insertion groove 2 can be held between the bolt 4 and the receiving implement 6. Further, the nut 4' is swung, the bending part 10' of the washer is rolled into a flat plate shape between an opposite surface 7' of the body 7 of the nut 4' and an opposite surface 8' of the head part 8 of the bolt 4 and, thereby, the fastening state of the steel material 11 is confirmed.