An apparatus which determines activeness/inactiveness of bacteria in real time by measuring a specific light emission spectrum upon performing sterilization using plasma to highly efficiently sterilize is provided. As solving means, plasma is irradiated on a processing target from a plasma source connected to an alternate-current power supply and light emission of the processing target caused by the irradiation of plasma is detected by a light emission intensity detector unit. Particularly, by detecting wavelength intensity of hydrogen or hydroxyl group, activeness/inactiveness of bacteria can be determined at an early stage. Thus, an appropriate output of a power supply for sterilization can be controlled.
