A fishing reel gear attachment structure for a fishing reel reciprocating mechanism, the fishing reel gear attachment structure configured to receive rotation of a handle, the fishing reel gear attachment structure comprising: a traverse cam shaft (21, 221, 321) including a shaft body including intersecting helical grooves on an outer peripheral surface thereof, the shaft body including a longitudinal end, a gear support portion including a circular cross-section, the gear support portion configured on the longitudinal end, and a gear engaging portion including a non-circular cross-section, the gear engaging portion including first and second opposed portions and first and second straight portions on a surface thereof, the first opposed portion configured opposite to the second opposed portion across a cross-sectional center of the gear engaging portion, the first and second opposed portions being coupled to the first and second straight portions, respectively; and a metal gear component (23, 223, 323) including a gear portion configured on an outer peripheral surface of the gear component, the gear portion configured to receive rotation of the handle, an axis aligned portion configured on an inner peripheral surface of the gear component, the axis aligned portion being fitted to the gear support portion, an axis of the gear component being aligned with an axis of the traverse cam shaft, and a coupling portion coupled to the gear engaging portion in a unitarily rotatable state, the coupling portion including a slot configured on a first end surface of the gear component, the slot engaged with the first and second straight portions, wherein the gear component includes a boss protruding from the first end surface, the boss includes a protruding end surface, and the slot is formed on the protruding end surface, characterised in that the slot being formed across a diameter of the boss a traverse cam shaft (21, 221, 321) including a shaft body including intersecting helical grooves on an outer peripheral surface thereof, the shaft body including a longitudinal end, a gear support portion including a circular cross-section, the gear support portion configured on the longitudinal end, and a gear engaging portion including a non-circular cross-section, the gear engaging portion including first and second opposed portions and first and second straight portions on a surface thereof, the first opposed portion configured opposite to the second opposed portion across a cross-sectional center of the gear engaging portion, the first and second opposed portions being coupled to the first and second straight portions, respectively; and a shaft body including intersecting helical grooves on an outer peripheral surface thereof, the shaft body including a longitudinal end, a gear support portion including a circular cross-section, the gear support portion configured on the longitudinal end, and a gear engaging portion including a non-circular cross-section, the gear engaging portion including first and second opposed portions and first and second straight portions on a surface thereof, the first opposed portion configured opposite to the second opposed portion across a cross-sectional center of the gear engaging portion, the first and second opposed portions being coupled to the first and second straight portions, respectively; and a metal gear component (23, 223, 323) including a gear portion configured on an outer peripheral surface of the gear component, the gear portion configured to receive rotation of the handle, an axis aligned portion configured on an inner peripheral surface of the gear component, the axis aligned portion being fitted to the gear support portion, an axis of the gear component being aligned with an axis of the traverse cam shaft, and a coupling portion coupled to the gear engaging portion in a unitarily rotatable state, the coupling portion including a slot configured on a first end surface of the gear component, the slot engaged with the first and second straight portions, a gear portion configured on an outer peripheral surface of the gear component, the gear portion configured to receive rotation of the handle, an axis aligned portion configured on an inner peripheral surface of the gear component, the axis aligned portion being fitted to the gear support portion, an axis of the gear component being aligned with an axis of the traverse cam shaft, and a coupling portion coupled to the gear engaging portion in a unitarily rotatable state, the coupling portion including a slot configured on a first end surface of the gear component, the slot engaged with the first and second straight portions, wherein the gear component includes a boss protruding from the first end surface, the boss includes a protruding end surface, and the slot is formed on the protruding end surface, characterised in that the slot being formed across a diameter of the boss