A collimated line beam is incident at an oblique incident angle of 0.61 rad into an inner surface of a hydrodynamic bearing whose inner diameter and length are 3 mm and 3.5 mm, respectively. Lights reflected in specified directions from the inner surface are selected to obtain an optical field whose phase distribution is proportional to the inner surface profile. This optical field interferes with a reference optical field in a two-wavelength interferometer using a tunable external cavity laser diode. Shapes of grooves with depth of about 5 mu m and width of about 0.15 mm formed on the inner surface can be measured with an error less than 0.3 mu m.