To reduce the number of automatic valves and pipes to be arranged in a membrane filter apparatus to lower the cost of a membrane filter apparatus body and to reduce the number of the automatic valves not only to simplify an electric control circuit but also to lower the incidence ratio of trouble.

The membrane filter apparatus is equipped with a membrane module 10 for filtering raw water, a backwashing water tank 2 for storing the purified water filtered by the membrane module 10 and a purified water backwashing pipe 21, which is not only the passage for connecting the membrane module 10 and the backwashing water tank 2 to send purified water to the backwashing water tank 2 but also a passage for supplying the purified water stored in the backwashing water tank 2 to the membrane module 10 by a backwashing pump 23 in order to wash the membrane module 10 and provided with the backwashing pump 23.