An automatic analyzer, comprising: a nozzle having an elongated shape in a vertical direction, the nozzle having a nozzle root in which the diameter of the nozzle is substantially constant and a nozzle tip having a tapered section attached to a straight section, wherein the straight section has a diameter that is smaller than the constant diameter of the nozzle root, wherein the nozzle can be elastically deformed in a horizontal direction and sucks and discharges a reagent for a blood clotting reaction; a nozzle driving mechanism that changes the position of the nozzle; and a control section that controls the suction and discharge of the reagent by the nozzle and controls the motion of the nozzle driving mechanism; wherein the automatic analyzer further comprises a clotting time detection section that is mounted with a reaction vessel in which a sample and the reagent are mixed and detects the clotting time of the sample, the control section presses the nozzle against the side surface of the inner wall of the reaction vessel by driving the nozzle in a given amount in the horizontal direction toward the side surface of the inner wall of the reaction vessel with respect to the reaction vessel into which the sample has been dispensed in advance such that a side surface of the root of the nozzle is brought into contact with said side surface and is elastically deformed in the horizontal direction of the nozzle, and discharges the reagent into the reaction vessel in a state where the side surface of the root of the nozzle is pressed against the side surface of the inner wall of the reaction vessel and the tip of the nozzle is prevented from coming into contact with the inner wall of the reaction vessel, wherein the reagent and the sample are stirred by the momentum of the discharged reagent without using an additional stirring mechanism. a nozzle having an elongated shape in a vertical direction, the nozzle having a nozzle root in which the diameter of the nozzle is substantially constant and a nozzle tip having a tapered section attached to a straight section, wherein the straight section has a diameter that is smaller than the constant diameter of the nozzle root, wherein the nozzle can be elastically deformed in a horizontal direction and sucks and discharges a reagent for a blood clotting reaction; a nozzle driving mechanism that changes the position of the nozzle; and a control section that controls the suction and discharge of the reagent by the nozzle and controls the motion of the nozzle driving mechanism; wherein the automatic analyzer further comprises a clotting time detection section that is mounted with a reaction vessel in which a sample and the reagent are mixed and detects the clotting time of the sample, the control section presses the nozzle against the side surface of the inner wall of the reaction vessel by driving the nozzle in a given amount in the horizontal direction toward the side surface of the inner wall of the reaction vessel with respect to the reaction vessel into which the sample has been dispensed in advance such that a side surface of the root of the nozzle is brought into contact with said side surface and is elastically deformed in the horizontal direction of the nozzle, and discharges the reagent into the reaction vessel in a state where the side surface of the root of the nozzle is pressed against the side surface of the inner wall of the reaction vessel and the tip of the nozzle is prevented from coming into contact with the inner wall of the reaction vessel, wherein the reagent and the sample are stirred by the momentum of the discharged reagent without using an additional stirring mechanism.