A structure of a tang of a roll-up tape measure includes a tang base and a tang plate formed at one side of the tang base. The tang base includes a plurality of tang coupling slots formed in one side thereof for coupling a measure ribbon and for positional adjustment of a reference point and also includes a tang hook formed at one end thereof. The tang hook includes a first hook section and a second hook section extending in opposite direction. The tang plate includes a receiving slot formed in one side thereof. The receiving slot receives and retains a magnetic element. The receiving slot includes, at one side thereof, at least one magnetic element for constraining and preventing the constraint stop from detachment.