To provide an indicator for displaying the completion of the connection of piping, and the connecting structure of piping, capable of informing that the connection of piping is surely completed to a worker.

This indicator 10 of a tubular structure is slidably mounted on an indicator mounting part 23 of female piping 20. As a first projecting part 11 and a second projecting part 12 of the indicator 10 are kept into contact with a female projecting part 22, the slipping-off of the indicator 10 from the female piping 20 can be prevented. When the connection of the female piping 20 and the male piping 30 is completed, a flare part 24 is fixed to a curved wall 41 through a garter spring 50, which prevents the separation of both piping 20, 30. The indicator 20 is locked over both piping 20, 30 in a state that its claw 13 is engaged with a cut part 42 of a cage 40 mounted on the male piping 30, and the first projecting part 11 is locked by the female projecting part 22.