The present invention provides a novel diazepine compound that blocks the IKur current or the Kv1.5 channel potently and more selectively than other K+ channels. The present invention relates to a diazepine compound represented by General Formula (1) or a salt thereof, wherein R1, R2, R3, and R4 are each independently hydrogen, lower alkyl, cyclo lower alkyl or lower alkoxy lower alkyl； R2 and R3 may be linked to form lower alkylene； A1 is lower alkylene optionally substituted with one or more substituents selected from the group consisting of hydroxyl and oxo； Y1 and Y2 are each independently -N= or -CH=； and R5 is group represented by (2) wherein R6 and R7 are each independently hydrogen or organic group； R6 and R7 may be linked to form a ring together with the neighboring group -XA-N-XB-； XA and XB are each independently a bond, lower alkylene, etc.
