Nuclear reactor vibration monitoring device and monitoring method thereof

According to an embodiment, a nuclear reactor monitoring device comprises: an ultrasonic wave transmission means which is installed on the outside surface of a reactor pressure vessel and transmits ultrasonic pulses to the interior of the reactor pressure vessel; an ultrasonic wave receiving means which is installed on the outside surface of the reactor pressure vessels and receives reflected pulses including ultrasonic waves from the ultrasonic pulses reflected by an inspection object in the reactor pressure vessel; a preprocessing means which specifies and removes the reflected ultrasonic pulses generated in the wall of the reactor pressure vessel from the reflected pulse signal received by the ultrasonic wave receiving means or selectively extracts the reflected pulse signal; and a calculation means which determines the vibration of the inspection object from the reflection pulse signal processed by the preprocessing means in accordance with the observation time of the inspection object.