Ionization loss of negaton-position pair is calculated as a function of their distance. This result will be useful to measure the energy of a γ-ray above 1010 eV from the reduction of ionization near the origin of the created pair. The reduction is due to the interference between the electro-magnetic field of negaton and that of position. We adopted a similar method to that of Fermi who had treated the energy loss of single electron taking into account the polarizability of the medium. Our result is not so different from Čudakov's so far as the distance between negaton and position is small.