A seal structure is disclosed, wherein a casing 10 has an annular protrusion 11 making up a hole-formed portion of a through hole 12. The portion of a joint member 30 around a joint body 31 is wound with a band-shaped seal member 60. A first peripheral end portion 60a and a second peripheral end portion 60b of the seal member 60 are formed progressively upward in the direction from the engine compartment to the passenger compartment. In the process of inserting the joint body 31 and the seal member 60 into the through hole 12 of the casing 10, the first peripheral end portion 60a and the second peripheral end portion 60b of the seal member 60 are butted against each other in the peripheral direction. As a result, a gap is difficult to form between the first peripheral end portion 60a and the second peripheral end portion 60b.