To provide a quantitative evaluation by extensively conducting an objective inspection of surface conditions of a workpiece.

A feeler chip 12 guided on a surface 10 sends an electrical signal representing a waviness of the surface 10 to a measuring instrument 14. A measurement value is transmitted to an analog-to-digital converter 16, and is assigned to one of discrete measurement points. A calculation means 18 receives the measurement value to effect Fourier analysis of the measurement value. According to this analysis, a roughness profile is decomposed into a series of harmonic oscillation having certain wave frequency and amplitude. Then, the calculation means 18 combines components of the Fourier series to form a wave frequency band. An amplitude of each wave frequency band corresponds to an average amplitude of each wave frequency included in the frequency band. Results of this processing are indicated by an output means 20.