To provide a filter cleaning method for making a reclaimed filter which prevents the occurrence of film breakage in a conventional cleaning period and is sufficiently pure by raising a filter cleaning capacity and curtailing a cleaning period.

In the filter cleaning method, a filter for filtering a molten polyester composition used in a polyester film formation process after being used is cleaned and reclaimed. After the polyester composition adhered to the filter is heated and decomposed in the presence of a compound having a hydroxyl group, the filter is cleaned in a cleaning bathtub filled with a cleaning liquid composed of an alkali cleaning agent while ultrasonic cleaning is used together.