A method for processing an organosiloxane film includes loading a target substrate (W) with a coating film formed thereon into a reaction chamber (2), and performing a heat process on the target substrate (W) within the reaction chamber (2) to bake the coating film. The coating film contains a polysiloxane base solution having an organic functional group. The heat process includes a temperature setting step of setting an interior of the reaction chamber (2) at a process temperature by heating, and a supplying step of supplying a baking gas into the reaction chamber (2) set at the process temperature, while activating the baking gas by a gas activation section (14) disposed outside the reaction chamber (2).