To provide a fan filter device, in which velocity distribution of outlet air is very uniform.

A plurality of fans 32 are provided above a prefilter 31. Chambers 35 in the same number as the fans 32 are formed above the fan 32 partitioned by partition boards 34. A straightening part 40 includes a frame 41 of a straightening device connecting to a box frame 37, and the straightening device 42 is placed in the frame 41. Air outlet from the fan 32 temporarily flows in the chamber 35, and passes through a perforated plate 36 and the straightening device 42, and the velocity distribution of the air is made uniform. The air is cleaned by passing an air filter 52, and the velocity of the air is made more uniform by ventilation resistance of the air filter 52 and a perforated plate 53.