  We estimate the gravitational wave (GW) background from Population III (Pop
III) stars using the results from our hydrodynamic simulations (Suwa et al.
2007). We calculate gravitational waveforms from matter motions and anisotropic
neutrino emissions for single Pop III stars. We find that the GW amplitudes
from matter motions are dominant until just after bounce, but those from
neutrinos dominate later on at frequencies below $\sim 10$ Hz in the GW
spectrum. Computing the overall signal produced by the ensemble of such Pop III
stars, we find that the resultant density parameter of the GW background peaks
at the amplitude of $\Omega_\mathrm{GW}\sim 10^{-10}$ in the frequency interval
$\sim 1-10$ Hz. We show that such signals, depending on the formation rate of
Pop III stars, can be within the detection limits of future planned
interferometers such as DECIGO and BBO in the frequency interval of $\sim
0.1-1$ Hz. Our results suggest that the detection of the GW background from Pop
III stars can be an important tool to supply the information about the star
formation history in the early universe.
