An oscillating mechanism includes a first non-circular gear, a rotary cam and a slider. The first non-circular gear is a bi-lobe gear rotatable about an axis of the handle rotation. The rotary cam is rotatably mounted in the reel unit so as to be parallel with the first non-circular gear. The rotary cam includes a cam protrusion, and a multi-lobe second non-circular gear arranged so that a tooth corresponding to the minimum tip diameter of the second non-circular gear meshes with a tooth corresponding to the maximum tip diameter of the first non-circular gear. The number of teeth of the second non-circular gear is greater than that of the first non-circular gear. The slider is axially movably mounted to the spool shaft. The slider includes a cam groove engaging the cam protrusion. The present invention facilitates tight winding of fishing line in a shape closer to a cylindrical shape.