  We report on a discovery of a diffuse nebula containing a pointlike source in
the southern blowout region of the Cygnus Loop supernova remnant, based on
Suzaku and XMM-Newton observations. The X-ray spectra from the nebula and the
pointlike source are well represented by an absorbed power-law model with
photon indices of 2.2+/-0.1 and 1.6+/-0.2, respectively. The photon indices as
well as the flux ratio of F_nebula/F_pointlike ~ 4 lead us to propose that the
system is a pulsar wind nebula, although pulsations have not yet been detected.
If we attribute its origin to the Cygnus Loop supernova, then the 0.5-8 keV
luminosity of the nebula is computed to be 2.1e31 (d/540pc)^2 ergs/s, where d
is the distance to the Loop. This implies a spin-down loss-energy E_dot ~
2.6e35 (d/540pc)^2 ergs/s. The location of the neutron star candidate, ~2
degrees away from the geometric center of the Loop, implies a high transverse
velocity of ~1850 (d/540pc)(t/10kyr)^{-1} km/s, assuming the currently accepted
age of the Cygnus Loop.
