To provide a surfactant which is obtainable by using substantially no alkali metal, has excellent readhesion prevention ability of finely-pulverized particles at the time of cleaning, and is capable of quite efficient and advanced cleaning. In the present invention, a surfactant which comprises a neutralized salt (AB1) and/or neutralized salt (AB2) is used. Neutralized salt (AB1): a neutralized salt (AB1) which comprises an acidic compound (A1) containing at least each one of an acid group (X1) of an acid having the difference of heat of formation in an acid dissociation reaction (Q1) of 3 to 200 kcal/mol and a hydrophobic group (Y) containing 1 to 36 carbon atoms, and a nitrogen-containing basic compound (B) having the difference of heat of formation in a proton addition reaction of 10 to 152 kcal/mol, wherein (X1) is at least one species selected from a sulfonic acid group, and the like. Neutralized salt (AB2): a neutralized salt (AB2) which comprises a polymer (A2) having at least one acid group (X2) within the molecule, and the nitrogen-containing basic compound (B) having the difference of heat of formation in a proton addition reaction of 10 to 152 kcal/mol.