PROBLEM TO BE SOLVED: To provide an air filter unit which has high collection efficiency, is excellent in maintenance thereof and has a low pressure loss.SOLUTION: An air filter unit has at least two kinds of electret filter material connected in such a state that at least two kinds of the electret filter material are respectively subjected to pleat processing, forms a rectangular shape and has a frame body bonded and fixed to the whole periphery. Therein, the air filter unit satisfies the following conditions (1) and (2). (1) When a pressure loss at wind velocity 5.3 cm/s of an electret filter material in which a pressure loss at the wind velocity 5.3 cm/s is highest is A and a pressure loss at wind velocity 5.3 cm/sec of an electret filter material in which a pressure loss at the wind velocity 5.3 cm/sec is lowest is B, a relation of 2
