Abstract: A piston manufactured by combining different materials which is free from the problem of interfacial fracture in the interface between the different materials, and a manufacturing method for such a piston. The piston of an internal combustion engine includes a first portion containing a first material, a second portion containing a second material different from the first material, and a boundary portion containing both the first material and the second material, and joining the first portion and the second portion to each other by being provided between the first portion and the second portion by a prescribed thickness, wherein a composition ratio of the first material progressively decreases and a composition ratio of the second material progressively increases in the boundary portion from a side of the first portion to a side of the second portion. The boundary portion may be made by a layered additive manufacturing method.