A compound represented by the formula (I): wherein the partial structure (b) containing ring A: is a group of any of the following formulas: wherein X 1 ' is one kind selected from the following Group B; Group B: - Cy, - C(R x1 R x2 )-Cy, - C(R x1 R x2 )-C(Rx 3 R x4 )-Cy, - C(R x1 )=C(R x2 )-Cy, - O-Cy, - O-C(R x1 R x2 )-Cy, - C(R x1 R x2 -O-Cy, - S(O)n-Cy, - S (O) n-C (R x1 R x2 -Cy, - C(R x1 R x2 -S (O) n-Cy, - N(R x5 )-Cy, - N(R x5 )-C(R x1 R x2 )-Cy, - C(R x1 R x2 -N(R x5 )-Cy, - C(O)-N(R x5 )-Cy, - N (R x5 ) -C (O) -Cy, - S (O) m-N (R x5 )-Cy, - N (R x5 ) -S (O) m-Cy, and - O-S(O)m-Cy wherein n is an integer of 0 - 2; m is 1 or 2; Cy is a saturated or unsaturated cyclic group optionally having substituent (s) (optionally containing heteroatom(s)); R x1 , R x2 , R x3 , R x4 and R x5 are the same or different and each is a hydrogen, a C 1-6 alkyl group optionally having substituent (s) or a C 1-6 alkoxycarbonyl group optionally having substituent(s); and X 2 ' is an alkyl group optionally having substituent(s) (substituents are optionally joined to form a ring), Ar 1 is a C 6-10 aryl group optionally having substituent(s), a C 1-9 heteroaryl group optionally having substituent(s) R 1 is a hydrogen or a C 1-6 alkyl group optionally having substituent(s); R 2 is a hydrogen, a C 1-6 alkyl group optionally having substituent(s) or a C 2 - 6 alkenyl group optionally having substituent(s); R 3 is a hydrogen or a C 1-6 alkyl group; R 4 is a hydrogen or a C 1 - 6 alkyl group; R 5 is a hydrogen or a C 1 - 6 alkyl group; R 1 and R 2 are optionally joined to form a nitrogen-containing ring optionally having substituent(s); R 2 and R 3 are optionally joined to form cycloalkene or cycloalkane; R 4 and R 5 are optionally joined to form cycloalkane; or a pharmaceutically acceptable salt thereof. X 1 ' is one kind selected from the following Group B; Group B: - Cy, - C(R x1 R x2 )-Cy, - C(R x1 R x2 )-C(Rx 3 R x4 )-Cy, - C(R x1 )=C(R x2 )-Cy, - O-Cy, - O-C(R x1 R x2 )-Cy, - C(R x1 R x2 -O-Cy, - S(O)n-Cy, - S (O) n-C (R x1 R x2 -Cy, - C(R x1 R x2 -S (O) n-Cy, - N(R x5 )-Cy, - N(R x5 )-C(R x1 R x2 )-Cy, - C(R x1 R x2 -N(R x5 )-Cy, - C(O)-N(R x5 )-Cy, - N (R x5 ) -C (O) -Cy, - S (O) m-N (R x5 )-Cy, - N (R x5 ) -S (O) m-Cy, and - O-S(O)m-Cy - Cy, - C(R x1 R x2 )-Cy, - C(R x1 R x2 )-C(Rx 3 R x4 )-Cy, - C(R x1 )=C(R x2 )-Cy, - O-Cy, - O-C(R x1 R x2 )-Cy, - C(R x1 R x2 -O-Cy, - S(O)n-Cy, - S (O) n-C (R x1 R x2 -Cy, - C(R x1 R x2 -S (O) n-Cy, - N(R x5 )-Cy, - N(R x5 )-C(R x1 R x2 )-Cy, - C(R x1 R x2 -N(R x5 )-Cy, - C(O)-N(R x5 )-Cy, - N (R x5 ) -C (O) -Cy, - S (O) m-N (R x5 )-Cy, - N (R x5 ) -S (O) m-Cy, and - O-S(O)m-Cy wherein n is an integer of 0 - 2; m is 1 or 2; Cy is a saturated or unsaturated cyclic group optionally having substituent (s) (optionally containing heteroatom(s)); R x1 , R x2 , R x3 , R x4 and R x5 are the same or different and each is a hydrogen, a C 1-6 alkyl group optionally having substituent (s) or a C 1-6 alkoxycarbonyl group optionally having substituent(s); and X 2 ' is an alkyl group optionally having substituent(s) (substituents are optionally joined to form a ring), Ar 1 is a C 6-10 aryl group optionally having substituent(s), a C 1-9 heteroaryl group optionally having substituent(s) R 1 is a hydrogen or a C 1-6 alkyl group optionally having substituent(s); R 2 is a hydrogen, a C 1-6 alkyl group optionally having substituent(s) or a C 2 - 6 alkenyl group optionally having substituent(s); R 3 is a hydrogen or a C 1-6 alkyl group; R 4 is a hydrogen or a C 1 - 6 alkyl group; R 5 is a hydrogen or a C 1 - 6 alkyl group; R 1 and R 2 are optionally joined to form a nitrogen-containing ring optionally having substituent(s); R 2 and R 3 are optionally joined to form cycloalkene or cycloalkane; R 4 and R 5 are optionally joined to form cycloalkane; or a pharmaceutically acceptable salt thereof. <EOS>