  The most important uncertainty in the results of gravitational microlensing
experiments comes from the difficulties of photometry caused by blending of
source stars. Recently Nemiroff (1997) pointed out that the results of
microlensing experiments can also be affected by the blending of light from the
lens itself if a significant fraction of lenses are composed of stars. In this
paper, we estimate the effects of lens blending on the optical depth
determination and the derived matter distribution toward the Galactic bulge by
using realistic models of the lens matter distribution and a well-constrained
stellar luminosity function. We find that the effect of lens blending is
largest for lenses located in the Galactic disk. However, lens blending does
not seriously affect both the determination of the optical depth and the
Galactic matter distribution. The decrease in optical depth is $\sim 10%$ even
under the extreme assumption that lenses are totally composed of stars and disk
matter distribution follows a maximal disk model, in which the lens blending
effect is most severe.
