An encoding device including memory and a circuit. In operation, the circuit: encodes first vertex information, second vertex information, and third vertex information, the first vertex information indicating a position of a first vertex of a first triangle that is a triangle in a three-dimensional mesh and on a first plane, the second vertex information indicating a position of a second vertex of the first triangle, the third vertex information indicating a position of a third vertex of the first triangle; and encodes, as fourth vertex information indicating a position of a fourth vertex of a second triangle, (i) dihedral angle information indicating a dihedral angle formed by the first plane and a second plane and (ii) identifying information for identifying a position of a fifth vertex that is a virtual vertex of a third triangle.