The fatigue strength of a bottom end part jointed to an upper deck of a hull is sufficiently maintained to thereby improve fatigue life. In a tank cover which covers a protruding part of an independent spherical tank loaded in a ship with one part protruding above an upper deck of a hull, a bottom end part to be jointed to the upper deck is provided with a reinforced part which is reinforced for strength. The reinforced part is a thickened part with a thickness greater than a thickness of an other part. The reinforced part is provided on both ends in a direction along the width direction of the hull.