A compound of the formula: or its pharmaceutically acceptable salt, wherein R 1 is substituted or unsubstituted C 1 -C 10 straight or branched alkyl, substituted or unsubstituted C 2 -C 10 straight or branched alkenyl, substituted or unsubstituted C 2 -C 10 straight or branched alkynyl, substituted or unsubstituted C 3 -C 8 cycloalkyl, substituted or unsubstituted C 3 -C 8 cycloalkenyl or substituted amino, p is 1, and q and r are 0, a group of the formula: is a group of the formula: and R 2 is substituted or unsubstituted C 1 -C 10 straight or branched alkyl, substituted or unsubstituted C 3 -C 8 cycloalkyl, substituted or unsubstituted C 3 -C 8 cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted heterocyclyl, wherein the "substituted alkyl", "substituted alkenyl", "substituted alkynyl", "substituted cycloalkyl", "substituted cycloalkenyl", "substituted aryl", "substituted heteroaryl" or "substituted heterocyclyl" can be substituted at arbitrary position(s) with one or more group(s) selected from halogen, hydroxy, mercapto, nitro, nitroso, cyano, azide, formyl, amino, carboxy, C 1 -C 10 alkyl, C 1 -C 10 haloalkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, C 3 -C 8 cycloalkyl, C 3 -C 8 cycloalkenyl, aryl, heteroaryl, heterocyclyl, substituted carbamoyl, substituted sulfamoyl, substituted amidino, a group of the formula: -O-R 10, a group of the formula: -O-C(=O)-R 10, a group of the formula: -C(=O)-R 10, a group of the formula: -C(=O)-O-R 10, a group of the formula: -S-R 10 or a group of the formula: -SO 2 -R 10 (wherein R 10 is C 1 -C 10 alkyl, C 1 -C 10 haloalkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, C 3 -C 8 cycloalkyl, C 3 -C 8 cycloalkenyl, aryl, heteroaryl, heterocyclyl, carbamoyl, sulfamoyl or amidino), and wherein the term "aryl" refers to monocyclic or polycyclic aromatic carbocyclyl and monocyclic or polycyclic aromatic carbocyclyl fused with one or two 3- to 8-membered cyclic group(s), the term "heteroaryl" refers to a monocyclic or polycyclic aromatic heterocyclyl group containing one or more heteroatom(s) arbitrarily selected from O, S and N on the ring or a monocyclic or polycyclic aromatic heterocyclyl group fused with one or two 3- to 8-membered cyclic group(s) and the term "heterocylyl" refers to a non-aromatic heterocyclyl group containing one or more heteroatom(s) arbitrarily selected from O, S and N on the ring, or a non-aromatic heterocyclyl group fused with one or two 3- to 8-membered cyclic group(s). wherein R 1 is substituted or unsubstituted C 1 -C 10 straight or branched alkyl, substituted or unsubstituted C 2 -C 10 straight or branched alkenyl, substituted or unsubstituted C 2 -C 10 straight or branched alkynyl, substituted or unsubstituted C 3 -C 8 cycloalkyl, substituted or unsubstituted C 3 -C 8 cycloalkenyl or substituted amino, p is 1, and q and r are 0, R 2 is substituted or unsubstituted C 1 -C 10 straight or branched alkyl, substituted or unsubstituted C 3 -C 8 cycloalkyl, substituted or unsubstituted C 3 -C 8 cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl or substituted or unsubstituted heterocyclyl, wherein the "substituted alkyl", "substituted alkenyl", "substituted alkynyl", "substituted cycloalkyl", "substituted cycloalkenyl", "substituted aryl", "substituted heteroaryl" or "substituted heterocyclyl" can be substituted at arbitrary position(s) with one or more group(s) selected from halogen, hydroxy, mercapto, nitro, nitroso, cyano, azide, formyl, amino, carboxy, C 1 -C 10 alkyl, C 1 -C 10 haloalkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, C 3 -C 8 cycloalkyl, C 3 -C 8 cycloalkenyl, aryl, heteroaryl, heterocyclyl, substituted carbamoyl, substituted sulfamoyl, substituted amidino, a group of the formula: -O-R 10, a group of the formula: -O-C(=O)-R 10, a group of the formula: -C(=O)-R 10, a group of the formula: -C(=O)-O-R 10, a group of the formula: -S-R 10 or a group of the formula: -SO 2 -R 10 (wherein R 10 is C 1 -C 10 alkyl, C 1 -C 10 haloalkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, C 3 -C 8 cycloalkyl, C 3 -C 8 cycloalkenyl, aryl, heteroaryl, heterocyclyl, carbamoyl, sulfamoyl or amidino), and wherein the term "aryl" refers to monocyclic or polycyclic aromatic carbocyclyl and monocyclic or polycyclic aromatic carbocyclyl fused with one or two 3- to 8-membered cyclic group(s), the term "heteroaryl" refers to a monocyclic or polycyclic aromatic heterocyclyl group containing one or more heteroatom(s) arbitrarily selected from O, S and N on the ring or a monocyclic or polycyclic aromatic heterocyclyl group fused with one or two 3- to 8-membered cyclic group(s) and the term "heterocylyl" refers to a non-aromatic heterocyclyl group containing one or more heteroatom(s) arbitrarily selected from O, S and N on the ring, or a non-aromatic heterocyclyl group fused with one or two 3- to 8-membered cyclic group(s).