A dense-winding capable oscillating mechanism that holds down manufacturing costs and ensures easy manufacturing precision. The spinning reel oscillating mechanism (6), for reciprocating the spool back and forth in cooperation with rotation of the handle attached to the reel unit-to which a fishing-line-guiding rotor is rotatively fitted-includes a pinion gear (12), a stepped gear unit (13) and a shifting mechanism (17). The pinion gear (12) rotates in cooperation with handle rotation. The stepped gear unit (13) includes a larger-diameter gear (19) meshing with the pinion gear (12) and a smaller-diameter gear (20) disposed concentric with the larger-diameter gear (19), for rotating unitarily with the larger-diameter gear (19). The shifting mechanism (17) has a driven gear (16) meshing with the smaller-diameter gear (20) and reciprocates the spool by rotation of the driven gear (16). |