A reel unit includes a frame, and first and second cover plates that are detachably mounted on both sides of the frame. The frame includes first and second side plates and a plurality of connectors that connect the first and second side plates. The first side plate includes a plate member and an annular member. The plate member includes a first opening in its inner peripheral portion. The plate member is made of a magnesium alloy, with an ellectrodeposition treatment being performed on a surface of the plate member. The annular member has a second opening through which the spool is adapted to pass, and a female threaded portion that is formed on an inner peripheral portion of the second opening. The annular member is harder than the surface of the plate member on which the electrodeposition treatment is performed.