Provided are a plasma sterilizing device and a method for generating a plasma in an elongated thin tube constituting a sterilizing object, and performing the sterilizing treatment of the interior of the elongated thin tube. The plasma sterilizing device and a method can sterilize even an elongated thin tube of an internal diameter of 5 mm or less efficiently, can prevent the inner wall of the elongated thin tube from being damaged, can suppress the danger of a secondary infection, and can suppress the contamination of the elongated thin tube by the sputtering of an electrode. The plasma sterilizing device comprises a container (2) capable of housing an elongated thin tube (1) or a sterilizing object and adjusting the internal pressure, and an electrode (5) arranged in at least one end portion of the elongated thin tube. The plasma sterilizing device is characterized in that a plasma is generated in the elongated thin tube by applying an AC voltage to the electrode such that the internal or external pressure of the elongated thin tube is adjusted to establish a predetermined pressure difference between the inside and the outside of the elongated thin tube.
