A reel unit 2 for a spinning reel includes a housing unit 2a, a lid portion 2b, and a returning member 28. The housing unit 2a includes a cylindrical portion 27 and a somewhat semicircular first flange portion 24a arranged behind the cylindrical portion 27. The lid portion 2b has a somewhat semicircular second flange portion 24b arranged behind and forming a gap 27b with the rear surface of the cylindrical portion 27. The lid portion 2b is detachably coupled to the housing unit 2a. The returning member 28 is detachably mounted in gap 27b and includes a plate-like arranging portion 28a disposed in gap 27b and a protrusion 28b gradually protruding from a front side of the arranging portion 28a to face the first flange portion 24a. The protrusion 28b has a first sloped surface 28c contactable with a bail tripping mechanism.