PURPOSE: To simplify a means for fixing a module to a filter fitting plate by fixing a pressing plate on the filter fitting plate and simultaneously sticking the bundling part of the module formed of many hollow yarn membrane filters to the filter fitting plate.

CONSTITUTION: A filter fitting plate 5 is provided so as to partitioning the inside of a casing main body. A bundling part 16 is fixed to this filter fitting plate and a module 6 formed of many hollow yarn membrane filters is hung to the bundling part. The top surface of the circumferential part of the bundling part 16 is formed into the same plane as the top surface of the fitting plate 5. This bundling part 16 is allowed to fall into the stepped through-hole 14 bored to the fitting plate 5 and stopped. Further a pressing plate 8 is fixed on the fitting plate 5 by providing the through-hole 14 having hole diameter shortened smaller than the outer dimension of the circumferential part of the bundling part 16 to the position correspondent thereto. As a result, a means for fixing the module to the filter fitting plate is simplified and work can be performed while utilizing a general tool.