  For a variety of on-going and planned gravitational-wave (GW) experiments, we
study expected constraints on the fraction ($f_{\rm PBH}$) of primordial black
holes (PBHs) in dark matter by evaluating the energy-density spectra of two
kinds of stochastic GW backgrounds. The first one is produced from an
incoherent superposition of GWs emitted from coalescences of all the binary
PBHs. The second one is induced through non-linear mode couplings of large
primordial curvature perturbations inevitably associated with the generation of
PBHs in the early Universe. In this paper, we focus on the PBHs with their
masses of $10^{-8}M_{\odot}\leq M_{\mathrm{PBH}} < 1M_{\odot}$, since they are
not expected to be of a stellar origin. In almost all ranges of the masses, we
show that the experiments are sensitive to constrain the fraction for $10^{-5}
\lesssim f_{\rm PBH} \lesssim 1$ by considering the GWs from coalescing events
and $10^{-13} \lesssim f_{\rm PBH} \lesssim 1$ by considering the GWs from
curvature perturbations. Exceptionally, only in a narrow range of masses for
$M_{\mathrm{PBH}} \simeq 10^{-7} M_{\odot}$, the fraction cannot be constrained
for $f_{\rm PBH} \lesssim 10^{-13}$ by those two GW backgrounds.
