  Cross sections and analyzing powers for proton elastic scattering from
$^{116,118,120,122,124}$Sn at 295 MeV have been measured for a momentum
transfer of up to about 3.5 fm$^{-1}$ to deduce systematic changes of the
neutron density distribution. We tuned the relativistic Love-Franey interaction
to explain the proton elastic scattering of a nucleus whose density
distribution is well known. Then, we applied this interaction to deduce the
neutron density distributions of tin isotopes. The result of our analysis shows
the clear systematic behavior of a gradual increase in the neutron skin
thickness of tin isotopes with mass number.

Nuclear Experiment