An organic fertilizer producing system for producing organic fertilizer from excreta of livestock or domestic animal by using larvae of Musca domestica (housefly), comprising: - a first nurturing-processing storage unit for nurturing or growing larvae hatched from eggs, - a plurality of second nurturing-processing storage units arranged below the first nurturing-processing storage unit, - a plurality of third nurturing-processing storage units arranged below the plurality of second nurturing-processing storage units, said excreta of livestock being decomposed with enzyme of said larvae while larvae are nurtured in each nurturing-processing storage unit, and excrete or produce an organic fertilizer base material, - a colleting section for collecting said organic fertilizer base material produced, and - a larvae collecting section for collecting grown larvae, the resulting collected larvae as well as said organic fertilizer base material produced being carried out of the system, characterized in that: - said first nurturing-processing storage unit has a dropping part adapted for dropping grown larvae onto said plurality of second nurturing-processing storage units covered with excreta of livestock, - each second nurturing-processing storage units has a dropping part adapted for dropping grown larvae onto said plurality of third nurturing-processing storage units covered with excreta of livestock, - said first, second, and third nurturing-processing storage units are adapted for performing the above processing several times until the final nurturing-processing storage unit, the larvae collecting section collecting grown larvae crawling out of said final nurturing-processing storage unit, wherein the first, second, third and final nurturing-processing units are adapted for allowing said larvae to crawl out of said nurturing-processing storage units. - a first nurturing-processing storage unit for nurturing or growing larvae hatched from eggs, - a plurality of second nurturing-processing storage units arranged below the first nurturing-processing storage unit, - a plurality of third nurturing-processing storage units arranged below the plurality of second nurturing-processing storage units, said excreta of livestock being decomposed with enzyme of said larvae while larvae are nurtured in each nurturing-processing storage unit, and excrete or produce an organic fertilizer base material, - a colleting section for collecting said organic fertilizer base material produced, and - a larvae collecting section for collecting grown larvae, the resulting collected larvae as well as said organic fertilizer base material produced being carried out of the system, - said first nurturing-processing storage unit has a dropping part adapted for dropping grown larvae onto said plurality of second nurturing-processing storage units covered with excreta of livestock, - each second nurturing-processing storage units has a dropping part adapted for dropping grown larvae onto said plurality of third nurturing-processing storage units covered with excreta of livestock, - said first, second, and third nurturing-processing storage units are adapted for performing the above processing several times until the final nurturing-processing storage unit, the larvae collecting section collecting grown larvae crawling out of said final nurturing-processing storage unit, wherein the first, second, third and final nurturing-processing units are adapted for allowing said larvae to crawl out of said nurturing-processing storage units.