1. A conversational processing method performed in an information processing apparatus capable of processing digital signals, the method comprising: extracting a referential expression from an input sentence; generating an intermediate referential expression representing modifying relations among words constituting the extracted referential expression; and searching an object corresponding to the generated intermediate referential expression within a preconfigured object search range, wherein the referential expression includes at least one word or a sentence including a combination of words used for explaining an object instructed by a user, the object indicating a thing or a person on which an operation is performed, wherein the intermediate referential expression is a form of graph or tree including a plurality of nodes, wherein the graph or the tree represents modifying relations among words constituting the extracted referential expression, and wherein an uppermost node represents a name of the object indicated by the user and lower nodes represent properties of the object or represents a modifier modifying the uppermost node or forming a relation between two other nodes.