  A theoretical light-curve model of the 1985 outburst of RS Ophiuchi is
presented based on a thermonuclear runaway (TNR) model. The system consists of
a very massive white dwarf (WD) with an accretion disk (ACDK) and a red giant
(RG). The early phase of the V light curve is well reproduced only by the
bloated WD photosphere of the TNR model on a 1.35 +/- 0.01 M_sun WD while the
later phase is dominated both by the irradiated ACDK and by the irradiated RG
underfilling the inner critical Roche lobe. The UV light curve is also well
reproduced by the same model with the distance of 0.6 kpc to RS Oph. The
envelope mass at the optical peak is estimated to be 2 x 10^{-6} M_sun,
indicating a rather high mass accretion rate of 1.2 x 10^{-7} M_sun yr^{-1}
between the 1967 and the 1985 outbursts. About 90% of the envelope mass is
blown off in the outburst wind while the residual 10% (2 x 10^{-7} M_sun) has
been left and added to the helium layer of the WD. The net increasing rate of
the WD mass is 1.2 x 10^{-8} M_sun yr^{-1}. Thus, RS Oph is certainly a strong
candidate for a Type Ia supernova progenitor.
