There is disclosed a large conductance calcium-activated K channel opener comprising a compound of the formula (I): wherein R1 is aminosulfonyl, alkylsulfonyl, etc., R2 is hydrogen or halogen, R3 and R4 are hydrogen, halogen, alkyl or alkoxy, Ring A is benzene, pyridine, etc., and Ring Q is pyrazol, isoxazol, etc., and Ring Q and Ring A may be combined to each other to form a fused ring of the formula: where X is S or O, R5 is halogen, alkyl, etc., and R3 and R4 are the same as mentioned above, or a pharmaceutically acceptable salt thereof as an active ingredient.