The positions of single Si atoms deposited onto the Si(111)7 x 7 surface have been investigated by using a scanning tunneling microscope. On a corner adatom side, the deposited single Si atoms were located around a line connecting a rest atom and a corner adatom, while on a center adatom side, they were widely spread. Semi-empirical molecular orbital calculations were also performed on the basis of a cluster model. The distribution of the calculated stable positions of deposited single Si atoms was consistent with the above-mentioned tendency of the experimentally-observed deposited atom distribution.