An abnormality diagnostic device selects a previously stored diagnostic measuring orbit (S110), and makes a machine to perform a specified operation for diagnosis so as to measure a driving power value of an actuator (S120). In S140, the abnormality diagnostic device compares the measured driving power value and a driving power value at the time of normal driving, and extracts a non-corresponding portion as a characteristic point based on a previously set determination criteria. When the extracting of the characteristic point is confirmed in S170, the abnormality diagnostic device compares the extracted characteristic point with a characteristic point predicted to occur in a driving power value at a time of occurring abnormality in a mechanism element, and calculates an evaluation index from a corresponding degree of both. When the evaluation index is a threshold value or more in S180, the abnormality diagnostic device estimates a mechanism element having an abnormality in S190.