mode meanwhile the ion generator b on the screen holder 4 starts to generate ions to neutralize substances carrying hazardous cations for air sterilization purpose along air circulation route defined by the rotation of the fan blades whereas a conduction of contact passage is formed by the first conductor c having two contacts on the screen holder 4 and the second conductor d on the rim 5 of the front screen 5 the second conductor d is disconnected from both contacts of the first conductor c to become in off position once the front screen 5 is removed meanwhile the cpu 8 prevents the fan blades 6 from being activated due to that the first conductor c is in off position to avoid risks of activating the fan blades 6 by an accidental touch of the switch furthermore as illustrated in fig5 in another preferred embodiment of the present invention each of the fan blades 6 is hollowed and placed instead a layer of active carbon filter 61 fixed with a plurality of rivets 62 or in other means to each fan blade 6 the active carbon filter 61 is made of any basic filter materials as long as it is perforated and adhered with active carbon e g.