To provide a method for opening apart filter plates suitably, and a filter press used for the method.

A plate opening machine 13 which moves forward the filter plate 12 is arranged on both sides of a plurality of the multi-aligned filter plates 12, supported by lateral frames 23. Further, after filtering a slurry, a target filter plate 12A is moved forward by the plate opening machine 13 and thereby opened apart from the adjacent filter plate 12B. The plate opening machine 13 has a first grasping arm 41 and a second grasping arm 42, both for grasping the target filter plate 12A and a pressing arm 43 for pressing the adjacent filter plate 12B. The adjacent filter plate 12B continues to be pressed by the pressing arm 43, while the target filter plate 12A is moved forward, held by the first grasping arm 41 and the second grasping arm 42.