1. A language understanding apparatus comprising: a storage section that stores: concept structure data indicating a correlation between a tree structure of a concept to be used in a domain and a concept representation specifying the concept to be used in the domain, frame definition data corresponding to the concept to be used in the domain and indicating a correlation between one or more semantic frames for representing the concept to be used in the domain by another concept, one or more variables to be used in the one or more semantic frames, and variable definition data indicating a concept to be used as a variable; a phrase interpreter that receives input utterance data detects a concept representation included in an utterance content indicated by the input utterance data by referring to the storage section, and reads information of a concept corresponding to the detected concept representation from the storage section; and a bidding section that; reads information on a variable of a semantic frame corresponding to the concept indicated by the information read by the phrase interpreter and information on a concept corresponding to the variable by referring to the storage section, and allocates by writing to a variable allocation table from the concept representation detected by the phrase interpreter, for each semantic frame read: a concept representation associated with a concept corresponding to each variable of the semantic frame or a subordinate concept of that concept, and a concept representation whose variable of another semantic frame is not written, and generates variable allocation table data indicating a bidding result.