A compound of formula: wherein A is a group of the following formula (A-1): R 1a and R 1b are the same or different and each independently C 1-6 alkyl which may be optionally substituted by 1 to 3 halogen atoms; m and n are each independently an integer of 0 to 5; X 1 is hydroxyl, or aminocarbonyl; Z 1 is a single bond, oxygen atom, sulfur atom, -SO-, -SO 2 -, or -N(R 3)-; R 2 is cyano, optionally substituted C 1-6 alkyl, optionally substituted C 3-7 cycloalkyl, optionally substituted C 6-10 aryl, optionally substituted C 7-16 aralkyl, optionally substituted heterocycle, optionally substituted heterocyclic C 1-6 alkyl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl-C 1-6 alkyl, or optionally substituted 5 to 7-membered cyclic amino; provided that if R 2 is cyano and optionally substituted 5 to 7-membered cyclic amino, then Z 1 is a single bond; R 3 is hydrogen atom, optionally substituted C 1-6 alkyl, optionally substituted C 3-7 cycloalkyl, optionally substituted C 6-10 aryl, optionally substituted C 7-16 aralkyl, optionally substituted heterocycle, optionally substituted heterocyclic C 1-6 alkyl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl, or optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl-C 1-6 alkyl; wherein the substituent group in the optionally substituted C 6-10 aryl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl, optionally substituted C 7-16 aralkyl, and optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl-C 1-6 alkyl in R 2 is selected from the group consisting of: halogen atom, cyano, hydroxy, C 1-4 alkoxy (in which the alkoxy may be optionally substituted by (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy, (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), C 1-4 alkylsulfonyl, C 3-6 cycloalkyl, C 3-6 cycloalkoxy, mono- or di-C 1-6 alkylamino, mono- or di-C 1-6 alkylcarbonylamino, mono- or di-C 1-6 alkylsulfonylamino, C 1-4 alkyl (in which the alkyl may be optionally substituted by (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy (in which the alkoxy may be optionally substituted by 1 to 3 halogen atoms), (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), C 1-6 alkylcarbonyl, carboxy, C 1-4 alkoxycarbonyl, and aminocarbonyl; or a pharmaceutically acceptable salt thereof. wherein A is a group of the following formula (A-1): R 1a and R 1b are the same or different and each independently C 1-6 alkyl which may be optionally substituted by 1 to 3 halogen atoms; m and n are each independently an integer of 0 to 5; X 1 is hydroxyl, or aminocarbonyl; Z 1 is a single bond, oxygen atom, sulfur atom, -SO-, -SO 2 -, or -N(R 3)-; R 2 is cyano, optionally substituted C 1-6 alkyl, optionally substituted C 3-7 cycloalkyl, optionally substituted C 6-10 aryl, optionally substituted C 7-16 aralkyl, optionally substituted heterocycle, optionally substituted heterocyclic C 1-6 alkyl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl-C 1-6 alkyl, or optionally substituted 5 to 7-membered cyclic amino; provided that if R 2 is cyano and optionally substituted 5 to 7-membered cyclic amino, then Z 1 is a single bond; R 3 is hydrogen atom, optionally substituted C 1-6 alkyl, optionally substituted C 3-7 cycloalkyl, optionally substituted C 6-10 aryl, optionally substituted C 7-16 aralkyl, optionally substituted heterocycle, optionally substituted heterocyclic C 1-6 alkyl, optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl, or optionally substituted 5 to 12-membered mono- or poly-cyclic heteroaryl-C 1-6 alkyl; halogen atom, cyano, hydroxy, C 1-4 alkoxy (in which the alkoxy may be optionally substituted by (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy, (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy, (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), C 1-4 alkylsulfonyl, C 3-6 cycloalkyl, C 3-6 cycloalkoxy, mono- or di-C 1-6 alkylamino, mono- or di-C 1-6 alkylcarbonylamino, mono- or di-C 1-6 alkylsulfonylamino, C 1-4 alkyl (in which the alkyl may be optionally substituted by (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy (in which the alkoxy may be optionally substituted by 1 to 3 halogen atoms), (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), (a) 1 to 3 halogen atoms, (b) C 1-4 alkoxy (in which the alkoxy may be optionally substituted by 1 to 3 halogen atoms), (c) carboxy, (d) C 1-4 alkoxycarbonyl, (e) C 7-16 aralkyloxycarbonyl, (f) mono- or di-C 1-6 alkylaminocarbonyl, (g) 5 to 7-membered cyclic aminocarbonyl, or (h) C 3-6 cycloalkyl), C 1-6 alkylcarbonyl, carboxy, C 1-4 alkoxycarbonyl, and aminocarbonyl;