A piston made of aluminum cast alloy having a main body section in an approximately cylindrical shape, atop face section provided and arranged so as to occlude one end of the main body section, and a pin boss section in which a pin hole is provided so as to penetrate through the main body section in a radial direction. The piston comprises an aluminum cast alloy containing Mg (Magnesium): equal to or less than 0.2 mass %, Ti (Titanium) 0.05-0.3 mass %, Si (Silicon): 10-21 mass %, Cu (Copper): 2-3.5 mass %, Fe (Iron): 0.1-0.7 mass %, Ni (Nickel): 1-3 mass %, P (Phosphorus): 0.001-0.02 mass %, Al (Aluminum): the remaining portions, and impurities.