In an encounter vehicle determination apparatus, a probability of a host vehicle entering a host-vehicle intersection on a host-vehicle's course on a map-is estimated. A different-vehicle intersection on a course of a different vehicle on a map either (i) along the host-vehicle's course or (ii) from a connection road with the host-vehicle intersection to the host-vehicle's course is extracted within a predetermined range based on vehicle information acquired from the different vehicle via inter-vehicle communications. A probability of the different vehicle entering the different-vehicle intersection is estimated. A probability of encounter between the host vehicle and the different vehicle at the host-vehicle intersection is calculated from the estimated probabilities of (i) the host vehicle entering the host-vehicle intersection and (ii) the different vehicle entering the different-vehicle intersection. The different vehicle having the probability of encounter equal to or more than a threshold is determined to encounter the host vehicle.