A centrifugal separation type FFF device where a rotor can be rotated at a high speed safely so that particles of a smaller size in a sample liquid can be classified. A field flow fractionation device is provided with: a channel that is attached to the inner circumferential surface of the peripheral portion of a rotor and where a classification flow path is created; flow paths for feeding a sample liquid into and out from the classification flow path; and a rotational drive mechanism for rotating the rotational axis, wherein a channel installation portion is formed on one side of the peripheral portion, and a mass balancer portion for adjusting the mass distribution of the rotor is formed on the other side with the rotor base in between.