Disclosed is a medicament having a strong antibacterial activity against Gram-positive bacteria, Gram-negative bacteria, and resistant bacteria. A compound represented by formula [I] or a salt thereof is useful as an antibacterial agent. In formula [I], a bond containing a dotted line and connecting X2 to Y1 represents a single bond or a double bond； Z1, Z2, Z3, Z4, Z5, and Z6 each represent a nitrogen atom, formula: CH, or the like； X1 represents a C1-4 alkylene group which may be substituted by an oxo group； X2 represents a bonding hand or formula: CH； Y1 represents a spirocyclic group selected from a group of formulae (II)； X3 represents a C1-4 alkylene group, formula: NR10(CH2)m, formula: SOn, or a bonding hand； and R7 represents a C3-6 cycloalkyl group, a C3-6 cycloalkenyl group, an aryl group, a monocyclic heterocyclic group, a bicyclic heterocyclic group, or the like.
