PURPOSE: To select the interpretation of the input speech generation so as to secure a proper flow of a conversation by using the estimated effect secured with storage of the context of the speech generation.

CONSTITUTION: The speech generation type of the speech generation proposition contents is obtained by retrieving a speech generation type table 802. The expectant degree of the proposition contents is set at a low level in response to the proposition pattern included in a key slot of a completely concreted plan instance stored in a plan instance buffer 805. Meanwhile the expectant degree of the proposition contents is set at a high level in response to a key slot of a subgoal which is not turned into an instance or a plan instance which is not completely concreted. A voice comprehension control part 806 obtains the final score of each recognizing result P based on the expectant degree of the proposition contents as well as the speech generation type.