Optical tomographic images having high image quality are obtained by a light source of a simple structure that emits a plurality of discrete light beams. A first light beam (La) and a second light beam (Lb) having discrete wavelength bands (λ1 and λ2) are emitted form a light source unit (10), and enter a light dividing means (3). The light dividing means (3) separates the light beams (La and Lb) into a measuring light beam (L1a, L1b) and a reference light beam (L2a, L2b). The measuring light beams (L1a, L2a) are irradiated on a measurement target (S), and reflected light beams (L3a, L3b), which are reflected at various depth positions of the measurement target (S), are caused to enter a combining means (4). The reference light beams (L2a, L2b) propagate through an optical fiber (FB3) to enter the combining means (4). Interference light beams (L4a, L4b) formed by the reflected light beams (L3a, L3b) and the reference light beams (L2a, L2b) for each of the first and second light beams (La and Lb) are photoelectrically converted into interference signals (ISa, ISb). A tomographic image is obtained employing the interference signals (ISa, ISb) for each of the first and second light beams (La, Lb).
