An automatic analysis device, comprising: a nozzle from which a second liquid substance is discharged into a vessel storing a first liquid substance; a control unit (31, 43, 106) that is configured to control a horizontal position and the height of the nozzle in accordance with a liquid volume of the second liquid substance and a viscosity of the second liquid substance (Ml); a dispensing unit that is configured to use the nozzle to dispense the second liquid substance into the vessel; and a first detection unit that is configured to detect light with which a mixture of the first liquid substance and the second liquid substance is irradiated, wherein a discharge end of the nozzle is cut in an oblique direction, characterized in that the control unit (31, 43, 106) is configured to control the horizontal position and the height of the nozzle based on a relationship between the liquid volume of the second liquid substance to be discharged and a liquid volume of the first liquid substance in the vessel and a relationship between the viscosity of the second liquid substance and a viscosity of the first liquid substance, wherein if the liquid volume of the second liquid substance is more than that of the first liquid substance and the viscosity of the second liquid substance is equal to or lower than that of the first liquid substance, the nozzle is positioned at the middle of the reaction vessel and the nozzle is positioned at a height of a reference position; if the liquid volume of the second liquid substance is less than that of the first liquid substance and the viscosity of the second liquid substance is higher than that of the first liquid substance, the nozzle is positioned on the inner wall side of the reaction vessel and nozzle is positioned at a height lower than the reference position; if the liquid volume of the second liquid substance is less than that of the first liquid substance and the viscosity of the second liquid substance is equal to or lower than that of the first liquid substance, the height of the nozzle is set higher than the reference position with the nozzle positioned on the inner wall side of the reaction vessel; or if the liquid volume of the second liquid substance is more than that of the first liquid substance and the viscosity of the second liquid substance is higher than that of the first liquid substance, the nozzle is positioned on the inner wall side of the reaction vessel. a nozzle from which a second liquid substance is discharged into a vessel storing a first liquid substance; a control unit (31, 43, 106) that is configured to control a horizontal position and the height of the nozzle in accordance with a liquid volume of the second liquid substance and a viscosity of the second liquid substance (Ml); a dispensing unit that is configured to use the nozzle to dispense the second liquid substance into the vessel; and a first detection unit that is configured to detect light with which a mixture of the first liquid substance and the second liquid substance is irradiated, wherein a discharge end of the nozzle is cut in an oblique direction, characterized in that the control unit (31, 43, 106) is configured to control the horizontal position and the height of the nozzle based on a relationship between the liquid volume of the second liquid substance to be discharged and a liquid volume of the first liquid substance in the vessel and a relationship between the viscosity of the second liquid substance and a viscosity of the first liquid substance, wherein if the liquid volume of the second liquid substance is more than that of the first liquid substance and the viscosity of the second liquid substance is equal to or lower than that of the first liquid substance, the nozzle is positioned at the middle of the reaction vessel and the nozzle is positioned at a height of a reference position; if the liquid volume of the second liquid substance is less than that of the first liquid substance and the viscosity of the second liquid substance is higher than that of the first liquid substance, the nozzle is positioned on the inner wall side of the reaction vessel and nozzle is positioned at a height lower than the reference position; if the liquid volume of the second liquid substance is less than that of the first liquid substance and the viscosity of the second liquid substance is equal to or lower than that of the first liquid substance, the height of the nozzle is set higher than the reference position with the nozzle positioned on the inner wall side of the reaction vessel; or if the liquid volume of the second liquid substance is more than that of the first liquid substance and the viscosity of the second liquid substance is higher than that of the first liquid substance, the nozzle is positioned on the inner wall side of the reaction vessel.