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An atmospheric low-temperature plasma flow generated by a microwave discharge utilizing a coaxial cable for microwave transmission was utilized for the inactivation of a bacteria. The employed device consists of a cavity, a quartz discharge tube, a coaxial cable, a microwave power source, and a gas supply system. Using this argon plasma source, we attempted to clarify the effects of exposure temperature, exposure time, exposure distance, input power, and gas flow rate on the number of surviving cells of Escherichia coli. A log reduction number of E. coli of at least 2 (10-2) was obtained at an exposure temperature of 353 K when the exposure time was 600 s with a gas flow rate of 5 Sl/min and an input power of 400 W. The number of surviving cells decreased with an increase of exposure time under any sterilization condition.