1. An information processing apparatus comprising: a processor; a memory; an acquisition means for acquiring a plurality of pieces of information to be grouped, the pieces of information including time information as attribute information; and an arithmetic means for: grouping the pieces of information acquired by the acquisition means so that a portion in which a level of variation of intervals among times represented by the time information included in the pieces of information is greater than at least one threshold value is used as a boundary between groups, managing the pieces of information in form of a binary tree structure, and comparing, with the threshold value, a ratio between a standard deviation of intervals among times represented by time information included in information in a node of interest and a deviation of intervals among time information of child nodes having the node of interest as a parent node, the arithmetic means performs grouping so that pieces of information in the child nodes are handled as pieces of information in different groups or as information in a single group, wherein the arithmetic means uses a plurality of the at least one threshold value for the same pieces of information acquired by the acquisition means to obtain a plurality of grouped results which respectively have different finenesses.