A navigation server rapidly generating guide support information in view of a traffic state after occurrence of an accidental situation in a road section, and make a navigation device recognize the same. After occurrence of the accidental situation in a target road section, a changing pattern g2(t) of a cumulative traffic volume CQ of a second position x2 during a first period is estimated, on the basis of a value of a traffic volume Q1 of the target road section at the first time t1. Further, a primary guide support information during the first period is generated on the basis of a standard changing pattern g1(t) of the cumulative traffic volume CQ of the first position x1 and a changing pattern g2(t) of the cumulative traffic volume CQ of the second position x2 as the estimation result.