1. An optical tomographic imaging system configured to split light emitted from a wavelength sweep light source into measuring light and reference light, configured to radiate the measuring light onto a measuring subject, configured to combine reflection light from the measuring subject with the reference light, configured to detect interfered light obtained by combining the reflection light with the reference light as an interference signal, and configured to Fourier-transform the interference signal to acquire a tomographic image of the measuring subject, the optical tomographic imaging system comprising: a tomographic data generating unit configured to generate tomographic data of the measuring subject based on the interference signal; a surface data generating unit configured to carry out processing in parallel with the tomographic data generating unit and configured to generate surface data of the measuring subject based on the interference signal; a tomographic image constructing unit configured to construct a tomographic image that is based on the tomographic data generated by the tomographic data generating unit; a surface image constructing unit configured to construct a surface image that is based on the surface data generated by the surface data generating unit; a display image generating unit configured to generate a display image from the tomographic image and the surface image; and a frame thinning unit configured to carry out thinning processing on the interference signal on a frame-by-frame basis so that the interference signal is outputted at a frame rate equal to or less than a frame rate of a monitor device on which the tomographic image and the surface image are displayed, wherein the interference signal subjected to the thinning processing by the frame thinning unit is inputted to the tomographic data generating unit.