To manufacture a piston having an oil return passage for returning oil entering an oil ring groove to the crankcase side without using a drill.

A piston main body 10 has the top part 11 and the skirt part 12 forming a piston housing space 13 with the top part 11 by extending to the back face side of this top part 11. The skirt part 12 has the circular arc- shaped part 12a and the boss support wall part 12b formed by being dislocated inward in the radial direction from the outer peripheral surface of the top part 11, and when casting the piston main body 10, a groove 17 and a hole 18 are respectively formed on the inside of the circular arc-shaped part 12a and the outside of the boss support wall part 12b among a back face of the top part 11. The groove 17 and the hole 18 are respectively communicated with an oil ring groove 27 by cutting the oil ring groove 27 on the outer peripheral surface of the top part 11 to form an oil return passage.