A seal structure for the joint section between path forming members, configured in such a manner that a seal member is disposed between a first path forming member and a second path forming member, the seal member having a seal section mounted in an endless mounting groove provided in the surface of the first path forming member which is joined to the second path forming member. The seal member (12) is configured so as to integrally have: the seal section (12a); ear sections (12b) protruding sideward along a joint surface (10) from the portions of the seal section (12a) which are separated from each other in the peripheral direction; and protrusions (12c) respectively protruding from the ear sections (12b) in the direction opposite the direction toward a second path forming member (6) so as to be perpendicular to the joint surface (10). The joint surface (10) is provided with: recesses (21) adapted to respectively house the ear sections (12b) and connecting to the mounting groove (19); and press-fit holes (22) which each have one end open to the recess (21) and which allow the protrusions (12c) to be press fitted therein. The configuration facilitates the mounting of the seal member, prevents a mounting error, and provides a uniform tightening allowance over the entire periphery of the seal section.