Safety is extremely high, odorless, low environmental impact, keeping the food freshness, may be used in various applications in hazardous substances without generating, be contained in various products by combustion waste or the like, antibacterial an object to provide a high antimicrobial and antiviral agent having antiviral effect, an ultrafine particle shells was calcined formed by micronization, the minor axis direction of the number average length of the primary particles (a) is 10nm It solved the problem by antimicrobial and antiviral agent which is a ~ 100 nm. Furthermore, shells and fired after pre-ground and then, those 90% volume particle size was classified so as to 30μm or less, and finely pulverized to a volume average particle diameter is in the range of 0.5 ~ 10 m, then further solved the problem by antimicrobial and antiviral agents are those prepared by micronization by a wet method.