  Using the near-infrared (NIR) observations of the afterglows of the high
redshift ($5 \la z \la 25$) gamma-ray bursts (GRBs) which will be detected by
the {\it Swift} satellite, we discuss a way to study the cosmic reionization
history. In principle the details of the cosmic reionization history are well
imprinted in the NIR spectra of the GRB afterglows. However the spectroscopy
with a space telescope is required to obtain such an information for a very
high redshift ($z\ga 15$) unless the neutral fraction of the high-$z$ universe
is less than $10^{-6}$. The broad-band photometry has the higher sensitivity
than that of the spectroscopy, so that the NIR photometric follow-up of the GRB
afterglows is very promising to examine the cosmic reionization history. A few
minutes exposure with a 8-m class ground-based telescope of the afterglow of
the high-$z$ GRBs will reveal how many times the reionization occurred in the
universe.
