To prevent the looseness of a nut caused by vibration by a simple configuration.

In a joint 1 having a pair of arcuate sandwiching members 1a, 1b sandwiching a connection part of piping 2, 2 and a wing nut 18 having a screw part 18a to which a fastening screw member 16 having a screw 19a formed to fasten the arcuate sandwiching members 1a, 1b to each other with the piping 2 sandwiched is screwed and penetrated, and with wing nut operating parts 18b, 18b for rotating the screw part 18a, wing nut looseness prevention members 19, 19' are provided with supported members 21a, 21b supported by the arcuate sandwiching members 1a, 1b, screw sandwiching members 24, 27 for sandwiching the fastening screw member 16 penetrated through the fastening wing nut 18, and rotation regulation parts 22, 23, 28 for locking the wing nut operating parts 18b, 18b to regulate the rotation.