  We study the signature of primordial non-Gaussianity imprinted on the power
spectrum of the 21-cm line differential brightness temperature during dark
ages. Employing the perturbative treatment of gravitational clustering, we
quantitatively estimate the effects of the non-Gaussian and one-loop
corrections on the 21-cm power spectrum. The potential impact of the use of the
21-cm power spectrum for the constraint on local-type primordial
non-Gaussianity is investigated based on the Fisher matrix analysis. Our
results show that the 21-cm power spectrum for an array with a baseline of
several tens of kilometers can constrain the primordial non-Gaussianity to a
level severer than that from cosmic microwave background measurements and its
constraining power is stronger than that of the 21-cm bispectrum, while in the
ultimate situation the 21-cm bispectrum eventually becomes more powerful.
