A spinning reel rotor braking device has a moving member, a braking member, and a restriction mechanism. The moving member is provided on the rotor and movable between a first position and a second position as the bail arm moves. The braking member is mounted on the mounting groove of the reel unit, and has a drag portion that generates a braking force by frictionally sliding against the moving member when the moving member is in the second position. The restriction mechanism is formed on an inner periphery of the braking member and on an outer periphery of the mounting groove, and restricts backward movement of the braking member relative to the reel unit so that the braking member does not come into contact with a rear end portion of the mounting groove. With the present invention, the braking force of the rotor braking device can be stabilized.