  Results of simultaneous INTEGRAL and optical observations of galactic
microquasar SS433 in May 2003 and INTEGRAL/RXTE observations in March 2004 are
presented. Persistent precessional variability with a maximum to minimum
uneclipsed hard X-ray flux ratio of \sim 4 is discovered. The 18-60 keV X-ray
eclipse is found to be in phase with optical and near infrared eclipses. The
orbital eclipse observed by INTEGRAL in May 2003 is at least two times deeper
and apparently wider than in soft X-ray band. The broadband X-ray spectrum
2-100 keV simultaneously detected by RXTE/INTEGRAL in March 2004 can be
described by bremsstrahlung emission from optically thin thermal plasma with
kT\sim 30 keV. The optical spectroscopy with the 6-m SAO BTA telescope
confirmed the optical companion to be an A5-A7 supergiant. For the first time,
spectorscopic indications of a strong heating effect in the optical star
atmosphere are found. The measurements of absorption lines which are presumably
formed in the non-illuminated side of the supergiant yield its radial velocity
semi-amplitude K_v=132\pm 9 km/s. The analysis of the observed hard X-ray light
curve and the eclipse duration, combined with spectroscopically found optical
star radial velocity corrected for the strong heating effect, allows us to
model SS433 as a massive X-ray binary. Assuming that the hard X-ray source in
SS433 is eclipsed by the donor star that exactly fills its Roche lobe, the
masses of the optical and compact components in SS433 are suggested to be
M_v\approx 30 M_\odot and M_x\approx 9M_\odot, respectively. This provides
further evidence that SS433 is a massive binary system with supercritical
accretion onto a black hole.
