Provided are a co-occurrence word data generating unit configured to generate co-occurrence word data including a co-occurrence word that is a vocabulary used along with a predetermined keyword in posted data in all periods and an appearance frequency of the co-occurrence word, from among pieces of posted data posed in a plurality of different periods; and a related data generating unit configured to generate related data including the co-occurrence word as a usual related word when a temporal variation in the appearance frequency of the co-occurrence word is smaller than a first threshold value and the appearance frequency is higher than a second threshold value.