A spinning reel spool coupling structure has a pin insertion portion, an anti-rotation pin, a retainer, and an anti-rotation groove. The pin insertion portion has a through hole passing through the spool shaft. The anti-rotation pin includes a first anti-rotation portion, a fitting portion, and a second anti-rotation portion. The fitting portion adjoins the first anti-rotation portion, and fits into the pin insertion portion. The second anti-rotation portion extends from the fitting portion and has a diameter greater than that of the pin insertion portion. The retainer member prevents the anti-rotation pin from being detached from the spool shaft, is disposed on an outer peripheral side of the first anti-rotation portion, and has an axial length such that the retainer member contacts the spool shaft. The anti-rotation groove is formed to extend in a direction substantially perpendicular to a length of the spool shaft, and engages the second anti-rotation portion.
