The reasoning system by knowledge activation of the present invention stores shallow knowledge and deep knowledge in memories. The reasoning by the reasoning mechanism is executed using the shallow knowledge. In case of the shallow knowledge to be used in the reasoning is not stored, the deep knowledge is used in the execution of the reasoning. Based on the information which is obtained by the execution of the reasoning, shallow knowledge is newly acquired. The reasoning system by knowledge activation needs only a short time for reasoning. Even in the case where shallow knowledge which is necessary for fast reasoning is not stored, the execution of the reasoning is possible, and new shallow knowledge is easily obtainable.