Abstract: An exhaust system component structure is provided. The structure has an exhaust passage through which exhaust of an internal combustion engine passes, is configured by a plurality of exhaust components, and includes: an upstream pipe having an upstream passage constituting the exhaust passage; a downstream pipe having a downstream passage constituting the exhaust passage; a first fixing surface provided on the upstream pipe and a second fixing surface provided on the downstream pipe, fixed so that the upstream passage and the downstream passage are in communication with each other. A projection part projecting from the first fixing surface on an outer side of the upstream passage toward the downstream pipe is provided. The projection part is provided with a protrusion part projecting toward an outer side of the exhaust passage. A groove part is provided at a position facing the protrusion part in the downstream pipe.