KEKB is an asymmetric energy B factory with the highest luminosity in
 the world. The Belle group at KEKB has played an important role in
 establishing the Standard Model by precise test of Kobayashi-Maskawa
 model of quark mixing and CP violation in the various aspects
 together with BaBar.  If new physics exists at TeV energy scale, it
 is quite conceivable that deviations from the predictions of the
 Standard Model will be observed in the decays of heavy flavors such
 as B, D and tau. By increasing the luminosity of KEKB by a factor of
 ~50, the flavor physics will enter a new era of precision
 measurements in which the possibility of detecting new physics
 effects will be greatly improved.  For this purpose, upgrade of KEK
 to SuperKEKB is planned at KEK. This program can provide an excellent
 opportunity to examine the fundamental properties of CP violation and
 flavor mixing in new physics. In this talk, physics program and
 design of the machine and the detector will be reviewed.  Especially,
 our strategy to reach the luminosity close to 10^36 will be presented
 in detail.