A brake operation structure is mounted on a reel unit, and adjusts a braking force applied to a spool. This brake operation structure includes a mounting tube, an operation knob, and a screw member. The mounting tube is formed to project from the reel unit. The operation knob is formed in a closed-end tubular shape to accommodate the mounting tube. The screw member has two male threaded portions that have a tubular shape when coupled to one another. The operation knob is pivotably retained to the mounting tube when the screw member engages an outer peripheral portion of the mounting tube and an inner peripheral portion of the operation knob. The operation knob is prevented from falling off from the mounting tube, while allowing the operation knob to pivot stably relative to the mounting unit.