A spinning reel being configured to forwardly reel out a fishing line, comprising: a handle; a reel unit rotatably supporting the handle; a rotor being rotatably supported by the reel unit; a spool having a bobbin trunk about which the fishing line is wound by the rotor; a spool shaft on which the spool is mounted; and an oscillating mechanism being configured to reciprocate the spool in a back-and-forth direction by a rotation of the handle, the oscillating mechanism including a traverse cam shaft and a slider, the traverse cam shaft having intersecting helical grooves on a surface thereof, the traverse cam shaft being disposed in parallel to the spool shaft, the traverse cam shaft being configured to be rotated in conjunction with the rotation of the handle, and the slider including a slider body having a through hole penetrating therethrough in a direction perpendicular to the traverse cam shaft, the slider body being coupled to the spool shaft to be unitarily movable therewith at least in an axial direction, an engaging member having a shaft part and an engaging part, the engaging part being mounted to a tip end of the shaft part to be engaged with the helical grooves, the engaging member being formed in a rod shape, a first bearing having a fitted part, a protruding part, and a support hole, the fitted part being fitted into the through hole, the fitted part including a stepped surface on an end thereof abutting the protruding part, the support hole penetrating through the fitted part and the protruding part, the support hole rotatably supporting the shaft part, a retainer member retaining the first bearing, and a fixation member fixing the retainer member to the slider body, characterized in the engaging member being formed in a rod shape in order for a rear end of the shaft part to protrude out of the through hole the protruding part having a diameter smaller than a diameter of the fitted part, the protruding part protruding out of the through hole, and the retainer member retaining the first bearing at the stepped surface a handle; a reel unit rotatably supporting the handle; a rotor being rotatably supported by the reel unit; a spool having a bobbin trunk about which the fishing line is wound by the rotor; a spool shaft on which the spool is mounted; and an oscillating mechanism being configured to reciprocate the spool in a back-and-forth direction by a rotation of the handle, the oscillating mechanism including a traverse cam shaft and a slider, the traverse cam shaft having intersecting helical grooves on a surface thereof, the traverse cam shaft being disposed in parallel to the spool shaft, the traverse cam shaft being configured to be rotated in conjunction with the rotation of the handle, and the slider including a slider body having a through hole penetrating therethrough in a direction perpendicular to the traverse cam shaft, the slider body being coupled to the spool shaft to be unitarily movable therewith at least in an axial direction, an engaging member having a shaft part and an engaging part, the engaging part being mounted to a tip end of the shaft part to be engaged with the helical grooves, the engaging member being formed in a rod shape, a first bearing having a fitted part, a protruding part, and a support hole, the fitted part being fitted into the through hole, the fitted part including a stepped surface on an end thereof abutting the protruding part, the support hole penetrating through the fitted part and the protruding part, the support hole rotatably supporting the shaft part, a retainer member retaining the first bearing, and a fixation member fixing the retainer member to the slider body, characterized in the engaging member being formed in a rod shape in order for a rear end of the shaft part to protrude out of the through hole the protruding part having a diameter smaller than a diameter of the fitted part, the protruding part protruding out of the through hole, and the retainer member retaining the first bearing at the stepped surface