In a system having an interface which utilizes an electroencephalogram, device operations which are not intended by the user are reduced.An adjustment apparatus for an electroencephalogram distinction method is used for an electroencephalogram interface system. The system has a biological signal measurement section for acquiring an electroencephalogram signal from a user, and an electroencephalogram interface section for presenting via an output section a plurality of menu items of the manipulation menu in a regular order, distinguishing by a previously determined distinction method a component of an event-related potential which is contained in the electroencephalogram signal after each menu item is highlighted, and operating a device based on the distinguished event-related potential. The adjustment apparatus includes: an analysis section for determining a gradient of a waveform of the event-related potential before the menu item is highlighted and a determination section for comparing the gradient of the waveform as determined by the analysis section against a threshold value, and determining that the menu item corresponding to the gradient is a menu item which the user wishes to select based on a result of comparison.
