  The bright F8 V solar-type star upsilon Andromedae has recently been reported
to have a system of three planets of Jovian masses. In order to investigate the
orbital stability and mutual gravitational interactions among these extrasolar
planets, both forward and backward integrations from the latest observed
orbital elements for all three planets' orbits have been performed under the
coplanar assumption. We reconfirm that the middle and the outer planet have
strong interaction leading to large time variations in the eccentricities of
these planets, which was shown by the previous studies. However, we discuss the
validity of the ignorance of the innermost planet. We argue that this planetary
system is likely to be stable and oscillate around current orbital elements
since it was formed.
  We suggest that one possible way to produce these orbital elements: the
innermost planet has very low eccentricity but the outermost planet has high
eccentricity could be the interaction with the protostellar disc.
