A hub unit for use in electrically assisted bicycles has an improved effect to radiate heat from a stator. A hub (7) has inner teeth (66a) meshable with planetary gears (65) and a fixing support shaft (57) projecting from opposite ends of the hub and provided fixedly relative to a motor housing (5). The motor housing (5) has no cylindrical wall (8) covering the outer peripheral surface of the stator (3) but leaves the stator outer peripheral surface exposed to effectively release the heat generated by the windings of the stator.