PURPOSE: To reduce the occupancy area of a reinforcing part formed in a filtration part to a minimum by providing the four reinforcing parts having diameter 1.5W5 times the thickness of the filtration part at positions trisecting the length of the diagonal of a filter plate of the filter press.

CONSTITUTION: Many protrusions and recesses are engraved on one surface of a filter plate 1, and a peripheral edge part 3 is made thicker than a filtration part 2. When the filtration part 2 of the filter plate is square, four reinforcing parts 4 are provided in the range ±L1/3×0.2 from the center of positions respectively trisecting the length L1 of the two diagonals of the filtration part 2, namely at intervals of l1/l2=1/1.2W1.2/1. The reinforcing part 4 has a conical trapezoidal cross section, the diameter of the top face 5 is 1.5W5 times larger than the thickness of the filtration part 2, and the top face 5 is made flush with the upper face of the peripheral edge part 3 of the filter plate 1.