A plasma sterilizing device has a container for a long tubule to be sterilized, having an adjustable internal pressure, and an electrode provided at at least one end of the long tubule. The device is configured so that plasma is generated inside the long tubule by applying an alternating current voltage to the electrode in such a state that the pressure inside and outside of the long tubule can be adjusted, so that there is a predetermined difference in pressure between the inside and the outside of the long tubule.