Damage of a lining-member is prevented through mitigation of stress concentration due to difference in thermal expansion. A lining-structure of a lining-member is provided on a base material of an insertion tube for adding a chemical to a reaction vessel for leaching under high temperature and high pressure. The base material has tube and flange sections. The lining-member is provided on the base material and formed of different material from the base material, and has a tube-lining section provided on the tube and flange lining sections provided on the flange-section. A chamfer-section is formed on the flange-section. The tube-lining section is protruded to the same height as a flat surface of the flange lining section. The flange lining-section has a curved surface-section protruded toward the base material side on the chamfer-section and is welded to a protruding-section of the tube-lining section that protrudes from a slant surface of the chamfer-section.