A human body security inspection apparatus, a method of operating the same, and an associated filter device are disclosed. The human body security inspection apparatus includes a radiation beam exit configured for emitting a radiation beam; a beam guiding box configured for guiding the radiation beam; and a filter device configured between the radiation beam exit and the beam guiding box. The filter device includes a housing and a filter cage having a central axis. The filter cage is formed by arranging two or more pairs of filtering sheets, which are made of different materials and/or have different thicknesses, in an encircling way. The filter cage is rotatable about its central axis such that at least one pair of filtering sheets is capable of filtering the radiation beam to adjust an outputted dosage of the radiation beam of the human body security inspection apparatus.