An apparatus for monitoring thrombus formation wherein anticoagulated blood is flown through a channel simulating a blood vessel while releasing the anticoagulant treatment or promoting blood coagulation to thereby monitor thrombus formation. This apparatus for monitoring thrombus formation comprises: a thrombus formation chamber in at least a part of which a thrombus formation inducer inducing thrombus formation is provided; an inlet tube which is connected to the thrombus formation chamber and through which blood is flown into the thrombus formation chamber; and a drug tube which is connected to the inlet tube and through which a drug releasing the anticoagulant treatment or a drug promoting blood coagulation is supplied. A method of monitoring thrombus formation which comprises flowing anticoagulated blood into a thrombus formation chamber, in at least a part of which a thrombus formation inducer inducing thrombus formation is provided, while releasing the anticoagulant treatment or promoting blood coagulation to thereby monitor thrombus formation.