A film forming method includes a step of arranging a wafer, on which an insulating film is formed, in a processing chamber of a film forming apparatus and a surface modification step of supplying a compound gas containing silicon atoms and an OH group-donating gas into the processing chamber so that Si—OH groups are formed on the surface of the insulating film. The film forming method further includes a film forming step of supplying a film forming gas containing a manganese-containing material into the processing chamber so that a manganese-containing film is formed on the surface of the insulating film on which the Si—OH groups have been formed through a CVD method.