  Under the assumption that the Milky Way's dark halo consists of primordial
black hole MACHOs (PBHMACHOs), the mass density of the halo can be measured by
the low frequency gravitational waves ($10^{-3} Hz \siml \nu_{gw} \siml
10^{-1}$ Hz) from PBHMACHO binaries whose fraction is $\sim 10^{-6}$. We find
that ten years observation by LISA will detect $\sim 700$ PBHMACHO binaries and
enable us to determine the power index of the density profile within 10% (20%)
and the core radius within 25% (50%) in about 90% (99%) confidence level,
respectively. The axial ratios of the halo may also be determined within $\sim
10%$. LISA and OMEGA may give us an unique observational method to determine
the density profile and the shape of the dark halo to open a new field of
observational astronomy.
