To obtain a new aromatic amidine derivative exhibiting a strong thrombin-inhibiting effect, having excellent duration in blood and excellent biological availability, suitable for oral administration and useful for as a selective thrombin inhibitor, etc.

The compound of formula I [(n) is 1-3; R1 is a (halogen- substituted) lower alkyl; R2 is H or a lower alkyl; R3 is a lower alkyl or a 3-7C cycloalkyl]. For example, 4-((R)-2-[[(S)-2-[2-(6-amidino-1-ethylinodol-2-yl) ethyl]pyrrolidinyl]carbonyl]-pyrrolidinyl}-(S)-2-(acetylamino)butanoic acid is obtained, for example, by reacting a compound of formula II (R2' is R2 or the like) with an acyl halide in the presence of a base in a solvent and subsequently converting the nitrile group of the obtained compound of formula III into an amidino group. The compound of formula III is new.