a reel unit including a reel body configured to be mounted on a fishing rod, a first opening on a side surface of the reel body, and a first lid member configured to cover the first opening;

a rotation transmission mechanism including a master gear shaft arranged along a direction of a first shaft axis extending in a lateral direction and rotatably mounted to the reel body and the first lid member, a master gear arranged on the master gear shaft and rotatably disposed about the first shaft axis, and a pinion gear arranged along a direction of a second shaft axis extending in a longitudinal direction and configured to mesh with a plurality of gear teeth of the master gear;

a handle assembly rotatably coupled to the master gear shaft;

a rotor rotatably mounted to the reel body about the second shaft axis, the rotation of the handle assembly being transmitted via the rotation transmission mechanism to the rotor;

a spool shaft movable relative to the reel body in the direction of the second shaft axis;

an oscillating mechanism configured to move the spool shaft back and forth in cooperation with the rotation of the handle assembly; and

a spool mounted to a fore end of the spool shaft and configured for a fishing line to be wound around an outer peripheral surface of the spool by the rotation of the rotor,

the reel body including a first rotation support portion that rotatably supports a portion of the master gear shaft between an interior side surface of the master gear and the inner side of the outer peripheral surface of the spool shaft, and

the first lid member including a second rotation support portion that rotatably supports the master gear shaft on a first lid member side of the master gear.