An apparatus for diagnosing abnormal operation of a rotor, comprising: a) a vibration sensor provided around a shaft in order to detect vibration occurring while the shaft provided in a rotor axially rotates and configured to output a vibration signal having acceleration indications periodically repeated on a cycle over time; b) a tachometer sensor configured to generate a periodic pulse signal over time whenever the shaft rotates once, the periodic pulse signal having pulse bars periodically repeated on the cycle per time; c1) a controller configured to determine an operation state of the rotor by receiving signals detected by the vibration sensor and the tachometer sensor, and when an aperiodic pulse signal is detected in the rotor, the controller determines a position of the rotor from which the aperiodic pulse signal is generated, wherein the time at which the aperiodic pulse occurs is converted into an angle of 360° and a display unit operated to display the position of the rotor in which the aperiodic pulse signal is generated; c2) the controller being configured to determine whether the current operation of the rotor is abnormal or normal by combining the vibration signal and the periodic pulse signal from the vibration sensor and the tachometer sensor and to determine that the current state of the rotor is normal when the signals are uniformly output; c3) the controller being configured to determine that the current operation of the rotor is abnormal when in the vibration signal detected by the combination of the signals from the vibration sensor and the tachometer sensor an aperiodic pulse is generated between the periodic pulse bars; and d) the display unit being configured to display the position of the rotor in which the aperiodic pulse signal is generated, according to information calculated by the controller. a) a vibration sensor provided around a shaft in order to detect vibration occurring while the shaft provided in a rotor axially rotates and configured to output a vibration signal having acceleration indications periodically repeated on a cycle over time; b) a tachometer sensor configured to generate a periodic pulse signal over time whenever the shaft rotates once, the periodic pulse signal having pulse bars periodically repeated on the cycle per time; c1) a controller configured to determine an operation state of the rotor by receiving signals detected by the vibration sensor and the tachometer sensor, and when an aperiodic pulse signal is detected in the rotor, the controller determines a position of the rotor from which the aperiodic pulse signal is generated, wherein the time at which the aperiodic pulse occurs is converted into an angle of 360° and a display unit operated to display the position of the rotor in which the aperiodic pulse signal is generated; c2) the controller being configured to determine whether the current operation of the rotor is abnormal or normal by combining the vibration signal and the periodic pulse signal from the vibration sensor and the tachometer sensor and to determine that the current state of the rotor is normal when the signals are uniformly output; c3) the controller being configured to determine that the current operation of the rotor is abnormal when in the vibration signal detected by the combination of the signals from the vibration sensor and the tachometer sensor an aperiodic pulse is generated between the periodic pulse bars; and d) the display unit being configured to display the position of the rotor in which the aperiodic pulse signal is generated, according to information calculated by the controller.