5-Membered heterocyclic compound

A compound represented by the formula (I):

• wherein
• ring A is a saturated or unsaturated 5-membered heterocycle containing, as a ring-constituting atom besides carbon atoms, at least one heteroatom selected from a nitrogen atom, an oxygen atom and a sulfur atom, the ring-constituting atoms X1 and X2 are the same or different and each is a carbon atom or a nitrogen atom, the ring-constituting atoms X3 and X4 are the same or different and each is a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom (provided that a pyrrole ring wherein X1 is a nitrogen atom is excluded from ring A), and when the ring-constituting atoms X3 and X4 are the same or different and each is a carbon atom or a nitrogen atom, each ring-constituting atom optionally has substituent(s) selected from an optionally substituted alkyl group, an acyl group, an optionally substituted hydroxy group, an optionally substituted mercapto group, an optionally substituted amino group, a halogen atom, a cyano group and a nitro group;
• ring B is a cyclic group containing X5 and X6 as ring-constituting atoms, X5 is a carbon atom or a nitrogen atom, and X6 is a carbon atom, a nitrogen atom, an oxygen atom or a sulfur atom;
• R1 is a cyclic group optionally having substituent(s);
• R2 is a substituent that X6 optionally has when X6 is a carbon atom or a nitrogen atom;
• R3 is an optionally substituted alkyl group, an acyl group, an optionally substituted hydroxy group, an optionally substituted mercapto group, an optionally substituted amino group, a halogen atom, a cyano group or a nitro group;
• R4 and R5 are the same or different and each is a hydrogen atom or an alkyl group, or R4 and R5 optionally form, together with the adjacent nitrogen atom, an optionally substituted nitrogen-containing hererocycle;
• m is 0 or 1, provided that ring B is an aryl group or a heteroaryl group, then m should be 1;
• and
• n is an integer of 0 to 3,
• or a salt thereof.