To provide a connecting element capable of easily preventing a mistake of attaching a hose to an incorrect connection member.

This connecting element comprises a first connecting member 4 for connecting a first hose 34, and a second connecting member 5 for connecting a second hose 35, to connect the hoses 34, 35. An inner diameter g of the first hose 34 is smaller than an inner diameter h of the second hose 35. The connecting members 4, 5 respectively have free ends 15, 16, and one hose 34, 35 can be slid on the connecting member 4, 5 from the free end 15, 16. According to this invention, the second connecting member 5 has a step portion 13, and a diameter of the step portion 13 is reduced from a first outer diameter b to a second outer diameter c toward the free end 16. The first outer diameter b is larger than the inner diameter g of the first hose.