The present invention is intended to acquire a tabulation result corresponding to changes in questions based on the knowledge that question contents are changed as time advances from a point of generation of a cause of the question and to acquire a tabulation result corresponding to questions issued from customers with question contents changing as time advances from a point of purchase of equipments, etc. Solution information for questions from customers is provided by forming a question group consisting of questions based on purchase of equipments, etc., by using the question group to tabulate the questions for each elapsed time period from a point of a cause of the question to a point of generation of the question, and by ranking the questions from the tabulation result.