Speech keywords are extracted from voice data on a response that an operator has made to an inquiry from a customer while referring to case data. Response keywords to be responded to the inquiry are extracted from the case data. After detecting a common keyword in the speech and response keywords, a support keyword is extracted from the speech keywords that appears in the response at a time near the appearance of the common keyword and that does not match the response keywords. Auxiliary data is stored which includes case identification information uniquely identifying the case data, a customer level indicating a knowledge level of the customer about the inquiry, and the support keyword.