An optical tomographic imaging apparatus acquires tomographic images of an object to be examined where the images are based on multiplexed reference light and return light returned from the object irradiated by measurement light via a scanning unit. The apparatus includes a splitting unit to split light irradiated from a light source into the measurement light and the reference light, and a focusing unit disposed on the optical path of the measurement light between the splitting unit and scanning unit. A primary magnification of the optical system on the optical path of the measurement light or the observation light path, and a numerical aperture of the light source irradiating the measurement light, are configured such that a maximum inclination of light rays included in the light flux of the measurement light is maintained within ±2 degrees of inclination with respect to the optical axis of the optical path.
