To solve the problem that a calculation time for calculating a range of a thundercloud gets enormous in the prior art, when conducting retrieval about meteorological cases in the past while taking physical spreading of the thundercloud into account.

A retrieval area of the thundercloud is assigned using a meteorological image data showing a thunder occurrence determining element in the present situation and a thunder occurrence risk, retrieval conditions for a position of the thundercloud and a time taking the area of the thundercloud into account are determined based on the retrieval area and the thunder occurrence determining element in the present situation, the thunder occurrence judge-determining element in the present situation within the retrieval area is compared with the meteorological data in the past, as to a collation target concerned in the thundercloud, then the meteorological data in the past is selected based on a comparison result, and the selected meteorological data in the past and the thunder occurrence determining element in the present are worked to calculate similarity between the meteorological data in the past and the thunder occurrence judge-determining element in the present, so as to prepare a retrieval result including the similarity and the worked meteorological data in the past.