A film forming method includes mounting a substrate on a mounting member after loading the substrate into a reaction chamber, adsorbing a compound of a first metal on a surface of the substrate by supplying a source gas containing the compound of the first metal into the reaction chamber, reducing the compound of the first metal adsorbed on the substrate by making a reducing gas contact therewith to thereby obtain a first metal layer, and alloying the first metal and a second metal to obtain an alloy layer of the first metal and the second metal by injecting the second metal into the first metal layer. The second metal is ejected from a target electrode facing the substrate by making a sputtering plasma contact with the target electrode, and at least a surface of the target electrode is formed of the second metal different from the first metal.