The present invention provides compounds having superior TAFIa inhibitory activity. They are dihydroimidazoquinoline compounds represented by the following formula (I) or pharmaceutically acceptable salts thereof: wherein R is a hydrogen atom or a C1-10 alkyl group； R1 is a hydrogen atom, a C1-10 alkyl group, a C3-8 cycloalkyl group or a substituent having the structure represented by the following formula Ia or Ib: where R3 is a C1-6 alkyl group； R4 is a C1-6 alkyl group, a C3-8 cycloalkyl group, or a benzyl group； and R2 is a hydrogen atom or a substituent having the structure represented by the following formula Ic or Id:
