  We calculate electromagnetic mass difference of mesons using a method
proposed by Duncan {\it et al}. The RG-improved gauge action and the
non-compact Abelian gauge action are employed to generate configurations. Quark
propagators in the range of $m_{PS}/m_{V}=0.76-0.51$ are obtained with the
meanfield-improved clover quark action. Chiral and continuum extrapolations are
performed and the results are compared with experiments. Finite size effects
are also examined. Quark masses are extracted from the measured spectrum. Our
preliminary values for light quark masses are $m_{u}^{\bar{MS}}(\mu =2 {GeV}) =
3.03(19)$ MeV, $m_{d}^{\bar{MS}}(\mu = 2 {GeV}) = 4.44(28)$ MeV,
$m_{s}^{\bar{MS}}(\mu = 2 {GeV}) = 99.2(52)$ MeV.
