1. A fundus oculi observation device comprising: a first image forming part configured to optically acquire data and form a 2-dimensional image of a surface of a fundus oculi of an eye based on the data; a second image forming part configured to optically acquire data and form a tomographic image of the fundus oculi based on the data; a display; a control means for controlling the display to display the 2-dimensional image and the tomographic image side by side; and a designating means for designating a lesion as a partial region on the displayed tomographic image, wherein the control means determines a corresponding position of the designated partial region of the tomographic image on the 2-dimensional image which is seen from the anterior side of the eye, and causes the display to display designated-position information of the determined position of the designated partial region within the 2-dimensional image, together with the 2-dimensional image.