A film forming method for a target object including a main surface and grooves formed in the main surface, includes a step of supplying of a first gas into the processing chamber, and a step of supplying a second gas and a high frequency power for plasma generation into the processing chamber to generate in the processing chamber a plasma of a gas including the second gas in the processing chamber. The first gas contains an oxidizing agent that does not include a hydrogen atom. The second gas contains a compound that includes one or more silicon atoms and one or more fluorine atoms and does not include a hydrogen atom. A film containing silicon and oxygen is selectively formed on the main surface of the target object except the grooves.