A support structure of a ship tank, the ship tank being a horizontal type circular cylindrical tank mounted on a ship and storing a liquefied gas, the support structure comprising: a curved surface facing an outer peripheral surface of the tank; and a support unit supporting the tank on the curved surface and extending in a circumferential direction of the tank, wherein the support unit includes: a plurality of tubular elements arranged in the circumferential direction of the tank such that an axial direction of each of the tubular elements coincides with a radial direction of the tank; a plurality of inner members each holding, on the outer peripheral surface of the tank, an end portion of a corresponding one of the tubular elements at the tank side; and a plurality of outer members each holding, on the curved surface, an end portion of a corresponding one of the tubular elements at an opposite side to the tank, wherein the plurality of inner members are fixed to the tank, the plurality of outer members are configured to be slidable on the curved surface in an axial direction of the tank, among the plurality of outer members, at least one outer member disposed near a lowest point of the tank is a restricted outer member whose movement in the circumferential direction of the tank is restricted, and among the plurality of outer members, outer members positioned at both sides of the restricted outer member are unrestricted outer members movable in the circumferential direction of the tank. a curved surface facing an outer peripheral surface of the tank; and a support unit supporting the tank on the curved surface and extending in a circumferential direction of the tank, wherein the support unit includes: a plurality of tubular elements arranged in the circumferential direction of the tank such that an axial direction of each of the tubular elements coincides with a radial direction of the tank; a plurality of inner members each holding, on the outer peripheral surface of the tank, an end portion of a corresponding one of the tubular elements at the tank side; and a plurality of outer members each holding, on the curved surface, an end portion of a corresponding one of the tubular elements at an opposite side to the tank, wherein the plurality of inner members are fixed to the tank, the plurality of outer members are configured to be slidable on the curved surface in an axial direction of the tank, among the plurality of outer members, at least one outer member disposed near a lowest point of the tank is a restricted outer member whose movement in the circumferential direction of the tank is restricted, and among the plurality of outer members, outer members positioned at both sides of the restricted outer member are unrestricted outer members movable in the circumferential direction of the tank. a plurality of tubular elements arranged in the circumferential direction of the tank such that an axial direction of each of the tubular elements coincides with a radial direction of the tank; a plurality of inner members each holding, on the outer peripheral surface of the tank, an end portion of a corresponding one of the tubular elements at the tank side; and a plurality of outer members each holding, on the curved surface, an end portion of a corresponding one of the tubular elements at an opposite side to the tank, wherein the plurality of inner members are fixed to the tank, the plurality of outer members are configured to be slidable on the curved surface in an axial direction of the tank, among the plurality of outer members, at least one outer member disposed near a lowest point of the tank is a restricted outer member whose movement in the circumferential direction of the tank is restricted, and among the plurality of outer members, outer members positioned at both sides of the restricted outer member are unrestricted outer members movable in the circumferential direction of the tank.