To provide a coupling structure which can prevent abrasion of gasket during transferring of powder, and thereby safely transfer the powder for a long time.

This coupling structure 10 has a coupler 12 for inserting an adaptor 11, and a fastening lever 26 provided with a cam part 31 rotatably pivoted to the coupler 12 and to be fitted to a recession 19 of the adaptor 11. When fastening, a flow passage 15 is formed. The coupling structure 10 has also a gasket 23 for airtightly sealing a portion between the adaptor 11 and the coupler 12; a fitting groove 21 formed on an inner wall side of the coupler 12 for locating the gasket 23 so as to be faced to the adaptor 11 and sandwiching the gasket 23 in respect to the adaptor 11; a protection wall 22 arranged in the fitting groove 21 so as to coat the inner peripheral surface of the gasket 23 while preventing its exposure to the flow passage 15.