Abstract: A reverse rotation preventing mechanism in a spinning reel for fishing is characterized in that a rotor is secured to a rotary quill, which is rotated by the turning of a handle in kinematic conjunction therewith; a reverse rotation prevention member having reverse rotation prevention engagement portions is rotatably supported concentrically to the quill; a reverse rotation prevention claw is supported by the body of the reel so as to be swingable, and can be engaged with one of engagement portions; and a roller-type one-way clutch is provided between the rotor and the reverse rotation prevention member. When the rotor is reversely rotated in such a direction as to wind a fishline, the clutch member connects kinematically the rotor to the reverse rotation prevention member.