PROBLEM TO BE SOLVED: To provide a wastewater membrane filtration system, in which a highly-efficient and low-cost treatment of wastewater including highly-concentrated suspended solids is possible.SOLUTION: A waste water membrane filtration system (1) to filtrate suspended solids in wastewater with a filtration membrane includes a filtration tank (11) pooling a wastewater target of filtration, a filtration membrane module (13) provided in the filtration tank and filtrating the wastewater with many porous filtration membranes (51), and a diffuser (61) installed on the lower side compared to the filtration membrane module in the filtration tank and supplying air (A) to wash the filtration surface of the filtration membrane of the filtration membrane module. A diffuser body (61a) forming an introduction space of air from the outside, and a cylindrically-shaped nozzle (61b) projectingly provided on the diffuser body and spouting air introduced into the introduction space to the inside of the filtration tank are
