A compound represented by the following general formula (1), or a salt thereof has serine protease inhibiting activity, and particularly excellent inhibiting activity against clotting factor VIIa. This compound or a salt thereof is useful as therapeutic and/or prophylactic agents for diseases associated with thrombus formation. [wherein R1 represents hydrogen, R2 represents optionally substituted phenyl, etc., R3 represents optionally substituted C6-10 aryl, etc.].