White noise is applied to a servocontrol system of a servomotor in order to measure a frequency characteristic of a mechanical component in an electric injection molding machine, and a signal from an encoder is applied to a fast Fourier converter. Data from the fast Fourier converter is applied to a memory unit, and the content of the memory unit is displayed on a display unit in the form of a board diagram. Repair announcement is issued when a deviation of the resonant frequency of each mechanical component with respect to data at an initial setting time exceeds a predetermined value.