To achieve a higher accuracy with a steeper envelope of an interference characteristic curve by partially altering the structure of the conventional low coherence interference measuring apparatus.

There are arranged a main light source as low-coherence light source, an interference optical system in which the luminous flux emitted from the main light source is divided to be guided to both a subject and a control object, while the subject light reflected on the subject and the control light reflected on the control object are made to overlap and caused interfere with each other, a support means for supporting the control object movably and a detection means to detect the intensity of the interference light produced from the subject light and the control light. Furthermore, a sub-light source, equipped with the center wavelength thereof different from that of the main light source, is provided and the luminous flux emitted from the sub-light source is made to overlap on the optical path of the luminous flux emitted from the main light source, before being divided in the optical path thereof by an integrated optical system. At this point, since beating is generated in the envelope of an interference characteristic curve attributed to the difference in the center wavelength between the two light sources a drop on both sides of a peak is produced, thereby making the inclination of the envelope steeper.