The spin-polarized metastable-atom deexcitation spectroscopy measurement for a perpendicularly magnetized surface is presented. This technique, which is extremely surface sensitive, has been used to investigate the magnetic properties of the vacuum side of Fe films on Cu(100). It is shown that the spin polarization of the outermost surface of Fe/Cu(100) at around the Fermi level is opposite to the majority spin of the film bulk. The spin polarization of the outermost Fe layer is found to be nearly constant in the Fe thickness range of 2--7 monolayers.