An electroencephalogram decision system determines, when finding electroencephalogram information representing an electroencephalogram obtained by an electrode unit placed on a region of interest that forms part of a subject's head satisfying a predetermined condition, that a target electroencephalogram, which is an electroencephalogram with a characteristic variation, should have been produced. The predetermined condition is selected from of detection conditions including a first type of condition and a second type of condition. The first type of condition specifies that a decision should be made, based on a component falling within a single frequency band included in the electroencephalogram represented by the electroencephalogram information, whether or not the target electroencephalogram has been produced. The second type of condition specifies that a decision should be made, based on components falling within multiple different frequency bands included in the electroencephalogram represented by the electroencephalogram information, whether or not the target electroencephalogram has been produced.