Low coherence light having a central wavelength .lamda.c of 1.1 .mu.m and a full width at half maximum spectrum .DELTA..lamda. of 90 nm is emitted. The low coherence light has wavelength properties suited for the light absorbing properties, the diffusion properties, and the dispersion properties of living tissue. A light dividing means divides the low coherence light into a measuring light beam, which is irradiated onto a measurement target via an optical probe, and a reference light beam that propagates toward an optical path length adjusting means. A multiplexing means multiplexes a reflected light beam, which is the measuring light beam reflected at a predetermined depth of the measurement target, and the reference light beam, to form coherent light. A coherent light detecting means detects the optical intensity of the multiplexed coherent light. An image obtaining means performs image processes, and displays an optical tomographic image on a display apparatus.