NOVELTY - The film-type treatment apparatus has an air diffuser unit (19) that is arranged in the bottom side of the membrane separation unit (18) to diffuse biogas in the methane fermentation tank (12). A discharge unit (23) discharges biogas received from a discharge port (22) into the digested sludge in the methane fermentation tank. A switching mechanism is switched to aeration state at which aeration of the biogas supplied to the membrane separation tank is performed and discharge state at which biogas in the methane fermentation tank is discharged.    USE - Film-type treatment apparatus for performing methane fermentation of organic substance such as excrement, purification tank sludge, sewage sludge, organic refuse and foodstuff type waste material.    ADVANTAGE - Aeration of the biogas within the methane-fermentation tank can be performed by switching mechanism to aeration state so that the digested sludge in methane-fermentation tank can be circulated between methane-fermentation tank and membrane separation tank through circular flow path. The necessity to stop drive of gas supply apparatus at the time of stirring methane-fermentation tank can be avoided. Temperature fall of gas supply apparatus can be prevented while continuing stirring in methane-fermentation tank so that generation of dew condensation within gas supply apparatus can be prevented. Damage to the film can be reduced by maintaining stirring in methane-fermentation tank so that the necessity of stopping and starting of gas supply apparatus can be reduced and wear and tear of gas supply apparatus can be suppressed. Quantity of the sediment settled and deposited on the bottom portion of membrane separation tank can be reduced so that the height of sediment can be maintained and aeration operation can be stabilized and washing of membrane separator can be performed uniformly.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for treatment method for performing methane fermentation of organic substance.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the film type methane fermentation treatment apparatus.    Methane fermentation tank (11)    Methane fermentation tank (12)    Membrane separation unit (18)    Air diffuser unit (19)    Discharge port (22)    Discharge unit (23)