1. An information presenting device for presenting a relationship between pluralities of data pieces, each plurality of data pieces being held by a respective one of a plurality of users, the information presenting device comprising: an acquiring unit operable to acquire at least (i) a first information group composed of a plurality of data pieces each held by a first user and attached with a first attribute and a second attribute, and (ii) a second information group composed of a plurality of data pieces each held by a second user and attached with the first attribute and the second attribute; a generating unit operable to, with respect to each of a plurality of values of the first attribute, extract data pieces having a same value of the first attribute from the first information group and the second information group, thereby generating a first subgroup consisting of the data pieces having the same value from the first information group, and a second subgroup consisting of the data pieces having the same value from the second information group; a calculating unit operable to, with respect to each of pair of generated first and second subgroups, each pair pertaining to a different one of the first attribute values, calculate a commonality between second attributes attached to the data pieces in the first subgroup and second attributes attached to the data pieces in the second subgroup in the pair; a determining unit operable to determine a presentation order in which to present all the calculated commonalities, based on how many data pieces the first and second subgroups in each respective pair contain; and a presenting unit operable to present the calculated commonalities arranged in the determined presentation order.