  We investigate the impact of the recent observation of the 21cm global signal
by EDGES on primordial power spectrum, particularly focusing on the running
parameters $\alpha_s$ and $ \beta_s$ which characterize the detailed scale
dependence of the primordial spectrum. When primordial power spectrum is
enhanced/suppressed on small scales, the structure formation proceeds
faster/slower and changes the abundance of small size halos, which affects the
sources of Lyman $\alpha$ radiation at high redshifts to alter the position of
the absorption line. Recent observation of EDGES detected the 21cm absorption
line at $z=17.2$ and this result also indicates that the brightness temperature
is consistent with zero for $z \lesssim 14$ and $z \gtrsim 22$, which can
exclude a scenario giving the absorption line at such redshifts. We argue that
the bound on the running parameters can be obtained by requiring that the
absorption line should not exceed observational bounds at such redshift ranges
and found that some parameter space of $\alpha_s$ and $\beta_s$ allowed by
Planck may be disfavored for some values of astrophysical parameters.
