To provide a method for operating a strainer that uses a centrifugal force generated by the rotation of a bottomed cylindrical vessel (3) having filtering holes (3d) in a side surface and can eliminate the clogging of the filtering holes and maintain the optimal straining effect while maintaining the optimal pressure and duration of pressing food ingredients, and to further provide an automatic strainer device. Provided is a method for operating a strainer, the strainer including: a vertical, bottomed cylindrical vessel that is supported so as to be rotatable around a central axis and has filtering holes bored in a circumferential plate rotary pressers (24, 25) that are located inside the bottomed cylindrical vessel and supported so as to be rotatable around the central axis while being in contact with or closer to an inner circumferential surface of the circumferential plate and a filtrate catching member that catches a filtrate discharged through the filtering holes of the bottomed cylindrical vessel to the outside of the vessel, the method including the step of, while rotating the bottomed cylindrical vessel, which contains an object to be strained input therein, in a predetermined rotation direction at a first rotation speed, rotating the rotary pressers in the same rotation direction as the bottomed cylindrical vessel at a second rotation speed different from the first rotation speed by a predetermined speed difference.
