To accomplish the sterilization processing of a material to be sterilized regardless of types thereof by eliminating the discoloring and damaging of surfaces due to plasma.

A mixed gas containing oxygen is converted to plasma with a first plasma generator 3 in a gas supply pipe 7 for supplying it into a sterilization chamber 1 while further being done so in the sterilization chamber 1 with a second plasma generator 5. The plasmas obtained are contained with a magnet 59 within the sterilization chamber 1 to eliminate an adverse effect such as damages or the like to the material 65 to be sterilized. On the other hand, a high-concentration plasma is formed by the plasmas contained by the magnet 59, thereby generating a large quantity of oxygen atoms for deactivating germs.