The fatty acid in the fatty acid sodium salt or fatty acid sodium/potassium mixed salt used in the soap of the present invention is a saturated or unsaturated fatty acid wherein the number of carbon atoms is preferably 8 to 20 and more preferably 12 to 18, and it may be either linear or branched.Specific examples include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, isostearic acid, and mixtures thereof, namely beef tallow fatty acid, coconut oil fatty acid, and palm kernel oil fatty acid.