  We present the spectral analysis of bright steady states in an outburst of
the transient neutron star low-mass X-ray binary (NS-LMXB) Swift J1858.6-0814
observed with NICER. We detected an ionized iron K absorption line (H-like Fe)
at 6.97keV in the spectrum. We estimated the photoionization parameter using
the ratio of the equivalent widths (EWs) of the FeXXVI (H-like) (17+\-5eV) and
FeXXV (He-like) (<3eV) and discuss the origin of the iron absorption line. The
irradiated gas producing the absorption line would locate within (3-6)*1E9cm
from the X-ray source. We suggest that the observed H-like Fe absorption line
originates from the highly-ionized gas in the inner accretion disk in Swift
J1858.6-0814.
