A reel body of a spinning reel includes a first opening formed in a rear end portion of the reel body, and a mounting portion formed on the periphery of the first opening. A first cover member and a second cover member can be selectively mounted on the mounting portion of the reel body such that the contour of either of the cover members is continuous with the contour of the reel body. The first cover member is mounted so as to close the first opening. The rear second cover member has a mounting portion and a rear drag mounting portion that is formed unitarily with the mounting portion. The rear drag mechanism can be mounted within the rear drag accommodating portion. With this invention, it is possible to form a reel unit of a spinning reel with an inexpensive structure without increasing the size of the reel unit.