1. A fundus oculi observing device, comprising: an optical system configured to split a low-coherence light into a signal light and a reference light and make the signal light propagated through a fundus oculi of an eye and the reference light propagated through a reference object interfere with each other to generate an interference light; a detector configured to detect the generated interference light and generate detection signals; a scanner configured to perform a scan of a target position with the signal light on the fundus oculi; an image forming part configured to form a tomographic image of the fundus oculi based on the detection signals generated during the scan; a specifying part configured to specify a characteristic site of the fundus oculi depicted in the formed tomographic image; and a controller configured to, based on a position of the specified characteristic site within a frame of the tomographic image, control the scanner to change the target position of the signal light so that the characteristic site is depicted in a predetermined position within the frame.