This optical tomographic imaging system comprises an optical path length adjustor configured to set a first reference position of a measurement depth direction to an inner edge of a measurement range by adjusting an optical path length of a reference light, and an optical path length switching unit having a preset optical path length that provides a second reference position differing in measurement depth from the first reference position by a predetermined amount and configured to change the optical path length of the reference light or the optical path length of the reflected light adjusted by the optical path length adjustor so as to switch between the first reference position and the second reference position. This system is capable of measuring a measurement region of interest at high resolution, regardless of the position (depth) of the measurement region of interest, in an SS-OCT employing a wavelength-swept light source.