A spinning-reel reel unit includes a rod-attachment leg and a reel body having a main piece and a lid member. The lid member is integrally formed with the rod-attachment leg and is attachably/detachably fitted to the main piece. The main piece and the lid member are shaped so that a joint forms a curved seam on the rod-attachment leg side. The joint is formed so as to bulge downward on a side of the main piece away from the rod-attachment leg. The joint is formed so as to be tilted upward on the rod-attachment leg aside toward the front. In the spinning-reel reel unit, the overall size of the reel is reduced while the strength of the reel unit is kept high.