This invention relates to an anti-dementia agent which uses a BEC 1 potassium channel inhibitor as the active ingredient. It was proved that the BEC 1 potassium channel inhibitor has an action to improve learning disorder and is useful as a preventive or therapeutic agent for diseases, preferably dementia, in which the BEC 1 potassium channel is considered to be concerned. Illustratively, it was confirmed by an in vivo test that the BEC 1 potassium channel inhibitor has an action to improve learning disorder. Also, it was found that a compound having 2,4,6-triamino-1,3,5-triazine has a BEC 1 potassium channel inhibitory action.