A judgment section (200) judges the presence or absence of a specific event-related potential in an event-related potential of user's (50) electroencephalogram measured by a biological signal detection section (101). A judgment standard storage section (203) stores a plurality of judgment standards according to the number of occurrences of the specific event-related potential. A user's state judging section (201) obtains the number of occurrences of the specific event-related potential by referring to a judgment result storage section (20) and selects any of the judgment standards in the judgment standard storage section (203) according to the obtained number of occurrences thereof for judgment.