PROBLEM TO BE SOLVED: To extract a precise frequency spectrum from an information amount related to rotation of a rotary apparatus such as a reduction gear provided in a multi-joint robot without depending on rotational speed.SOLUTION: In a frequency analytical method, an information amount related to rotation obtained from an input axis or an output axis of a rotary apparatus is acquired, and the acquired information amount related to rotation is fitted with a basic function using a rotational position of the input axis or the output axis of the rotary apparatus as a variable, and a frequency component related to rotation of the input axis or the output axis of the rotary apparatus is extracted based on the fitting result without being affected by rotational speed of the rotary apparatus.
