Abstract: A piston has a top surface composed of porous alumina. Top surface includes a first region and a second region. The first region includes a part or all of a region connecting to an outer periphery of the top surface. The second region is adjacent to the first region. The second region includes some or all of the region inside the top surface. The porous alumina formed on the second region is thinner than that formed on the first region. In a manufacturing method of a piston, first, a casting piston made of aluminum alloy is prepared. Then, a casting surface in a first region is removed, thereby a material surface is exposed. Then, anodization of the casting piston is performed, whereby a porous alumina is formed on the first and second regions.