1. A case accumulating apparatus, comprising: a storage device storing information about a set of correct answer cases; a learning device generating an inference rule while referencing the information stored in said storage device, and inferring a target characteristic from a known characteristic of a case to be inferred in compliance with the inference rule; an inquiry device inquiring of a user as to whether or not an inference result of said learning device is correct, and receiving a response from the user; and a control device determining the target characteristic of the case to be inferred based on the response, and adding information about the case to be inferred including the determined target characteristic to the set of correct answer cases.