In a broadcast receiver, determination is made, as channel search, whether a broadcast wave is valid for reception for all reception directions by a variable directional antenna with respect to only the frequency having the information stored as being invalid for reception in a storage unit. A second wrist element is rotatably provided on the first wrist element. The knowledge structures may be managed by users, wherein users may perform at least one of adding a new concept, creating a new relationship, confirming an existing relationship, and breaking an existing relationship.