An abnormal point locating method includes: a link primary abnormality judgment procedure that acquires information on a link through which each observation flow passes, locates a link through which an observation flow observed at an observation point passes, and judges whether the located link is normal or abnormal based on the observation flow; and a link secondary abnormality judgment procedure that judges a probability of abnormality based on a result of the link primary abnormality judgment procedure by using a connection relationship as seen from each observation point.