PURPOSE: To obtain a new benzoxazine derivative having excellent K+ channel function activities and useful as a medicine.

CONSTITUTION: This benzoxazine derivative is expressed by formula I [R1 and R2 each is H or an alkyl or R1 and R2 together denote polymethylene; R3 and R4 each is H, an alkyl, a haloalkyl, a halogen, an alkoxy, amino, an acylamino, nitro, cyano, an alkoxycarbonyl, etc.; R3 and R4 together denote N-O-N=; X is O, S or N-Z (Z is H, an alkyl, an aryl, OH, an alkoxy, cyano, etc.); Y is NR5R6; OR7 or SR8 (R5 and R6 each is H, OH, an alkoxy, an alkyl, etc.; R7 and R8 each is H, an alkyl or an aryl)], e.g. 6-bromo-7-chloro-N,2,2- trimethyl-2H-1,3-benzoxazine-4-carbonamide expressed by formula II. The compound expressed by formula I is obtained by directly reacting, e.g. a compound expressed by formula III (R9 is a lower alkyl) with an amine.