A level-of-confidence calculation apparatus includes a first collecting unit that collects relevant information related to first threat intelligence that is input; a second collecting unit that collects, from a memory unit storing threat intelligence to which a level of confidence is appended, second threat intelligence related to the relevant information; a generation unit that generates a graph in which the first threat intelligence, the relevant information, and the second threat intelligence are set as nodes and the nodes relating to related information are connected; and a calculating unit that calculates, by applying a belief propagation method to the graph, a level of confidence of the first threat intelligence based on a level of confidence of the second threat intelligence, and therefore a level of confidence of threat intelligence with uncertain level of confidence can be calculated.