It is an object of the present invention to produce a lightweight spinning reel master gear assembly to be assembled in a short period of time. A master gear assembly 9 is rotatably attachable to a reel unit 2 of a spinning reel. The master gear assembly 9 includes a master gear shaft 10 and a master gear 11. The master gear shaft 10 is rotatably attachable to the reel unit 2 and includes an attachment portion 10e having a male threaded portion 10f at least partially on the outer peripheral surface thereof. The mater gear 11 is fixed to the master gear shaft 10 while being integrally rotatable therewith. The master gear 11 includes a female threaded portion 11a screwed onto the male threaded portion 10f and a centered portion 11b with an axis appropriately aligned by the attachment portion.
