  We studied electronic states in vortex cores of slightly overdoped
Bi2Sr2CaCu2Ox by scanning tunneling spectroscopy. We have found that they have
stripe structures with a 4a0 width extending along the Cu-O bond directions.
Vortex core states are observed as two peaks at particle-hole symmetric
positions in the energy gap. Along a stripe, the peak positions of vortex core
states are constant and not influenced by the spatial variation of the energy
gap \Delta. Outer stripes have a larger energy than inner stripes. A mazelike
pattern in the electronic states at E = +-\Delta has been observed all over the
surface both inside and outside the vortex core. The orientation of stripes of
vortex core states was found to be related to the mazelike pattern in the
vortex core region. A short-range order of the mazelike pattern spatially
coexists with the superconductivity and locally breaks the symmetry of the two
Cu-O bond directions. We propose that the vortex core bound states are formed
by Bogoliubov quasiparticles owing to the depairing of Cooper pairs and have a
local C2 symmetry influenced by the short-range order of the mazelike pattern.
