An acquisition unit acquires a communication feature for normal communication of communication equipment. If a data count or a data acquisition period for the acquired communication feature exceeds a predetermined value, an amplification unit amplifies the data count for the communication feature by a plurality of predetermined schemes in accordance with data counts for respective groups, each group sharing a same 5-tuple. A creation unit creates, for each of the predetermined schemes, reference value information for normal communication of the communication equipment through learning using the amplified communication feature. A determination unit determines accuracy of abnormality detection for each of the predetermined schemes using an anomaly score representing a deviation of test data representing a communication feature for abnormal communication from the reference value information. A selection unit selects the reference value information created by one of the schemes, the determined accuracy for which is highest.