This invention relates to a 4-oxybenzopyran derivative of formula (I) wherein, R1 and R2 represent each independently a hydrogen atom, a C1-6 alkyl group or a phenyl group; R3 represents a hydroxyl group or C1-6 alkylcarbonyloxy group; R4 represents a hydrogen atom, a C3-6 cycloalkyl group, a C1-6 alkyl group, a C1-6 alkylcarbonyl group, a C1-6 alkylaminocarbonyl group, a di-C1-6 alkylaminocarbonyl group, an aryl group or a heteroaryl group; R5 represents a hydrogen atom or a C1-6 alkyl group; X is absent or represents C═O or SO2; R6 represents a hydrogen atom, a C1-6 alkyl group or a C3-6 cycloalkyl group; R7 represents a hydrogen atom, a halogen atom, a nitro group or a cyano group; or a pharmaceutically acceptable salt thereof. And this invention also relates to a drug for treating arrhytmia having the prolongation effect on the functional refractory period comprising said compound or a pharmaceutically acceptable salt thereof as an active ingredient.