PURPOSE: To provide a filter press and a filtration method of the filter press which is able to prevent the leakage of original liquid in advance, to detect the inability of filtration operation in advance, to prevent the unprepared prolongation of filtration operation time, and to conduct filtration operation smoothly.

CONSTITUTION: In a previous stage before starting filtration operation, the first fluid is supplied to each filtration chamber 16 to judge whether it is possible to maintain pressure within a specified range for a specified time. If the judgement is positive, the filtration is carried out by supplying original liquid after the discharge of the first fluid. On the other hand, if the judgement is negative, the cause is elucidated by the additional fastening of filter plates 14 or by the disassembly of the filter plates 14.