  We performed spectroscopic X-ray observations of the eastern and northern
regions of the Cygnus Loop with the ASCA observatory. The
  X-ray surface brightness of these regions shows a complex structure in the
ROSAT all-sky survey image. We carried out a spatially-resolved analysis for
both regions and found that $kT_{\rm e}$ did not increase toward the center
region, but showed inhomogeneous structures. Such variation cannot be explained
by a blast wave model propagating into a homogeneous interstellar medium. We
thus investigated the interaction between a blast wave and an interstellar
cloud. Two major emission mechanisms are plausible: a cloud evaporation model
and a reflection shock model. In both regions, only a reflection shock model
qualitatively explains our results. Our results suggest the existence of a
large-scale interstellar cloud. We suppose that such a large-scale structure
would be produced by a precursor.
