An observation allocating section exclusively allocates an observation point to each existing tracker in accordance with a distance between observation information acquired by an information acquiring section and observation information indicated by a predictive distribution. A hypothesis generating section generates a hypothesis likelihood and a hypothesis distribution, for each target tracker and for each hypothesis belonging to a hypothesis group including a first hypothesis and a second hypothesis. The first hypothesis is a hypothesis that the observation point is a result of observation of a subject target. The second hypothesis is a hypothesis that the observation point is not a result of observation of the subject target. The hypothesis likelihood is the likelihood of the hypothesis. The hypothesis distribution is the state distribution updated on the assumption that the hypothesis is correct.