An automatic analyzer comprising: a reaction disk, on which reaction cells for allowing a sample and a reagent to mix and react with each other are arranged on the circumference thereof, and which alternately repeats rotation and stop; a first reagent dispensing mechanism which dispenses the reagent into the reaction cell; a thermostat bath for controlling the reagent or a reaction solution in the reaction cell to have a constant temperature; a photometer which detects transmitted light or scattered light by irradiating light onto the reaction solution in the reaction cell; a reaction container supply section which supplies a disposable reaction container for allowing the sample and the reagent to mix and react with each other; a second reagent dispensing mechanism with a reagent heating function which dispenses the reagent into the disposable reaction container; a coagulation time detection section which detects transmitted light or scattered light by irradiating light onto the reaction solution in the disposable reaction container; a reaction container temperature control block which has the coagulation time detection section and is used for controlling the reagent or the reaction solution in the disposable reaction container to have a constant temperature; and a reagent dispensing syringe which is connected to the second reagent dispensing mechanism with a heating function; characterized by further including a fluid temperature control mechanism which is configured to control the temperature of an internal fluid of the reagent dispensing syringe by heating the fluid to a constant temperature and maintaining the temperature. a reaction disk, on which reaction cells for allowing a sample and a reagent to mix and react with each other are arranged on the circumference thereof, and which alternately repeats rotation and stop; a first reagent dispensing mechanism which dispenses the reagent into the reaction cell; a thermostat bath for controlling the reagent or a reaction solution in the reaction cell to have a constant temperature; a photometer which detects transmitted light or scattered light by irradiating light onto the reaction solution in the reaction cell; a reaction container supply section which supplies a disposable reaction container for allowing the sample and the reagent to mix and react with each other; a second reagent dispensing mechanism with a reagent heating function which dispenses the reagent into the disposable reaction container; a coagulation time detection section which detects transmitted light or scattered light by irradiating light onto the reaction solution in the disposable reaction container; a reaction container temperature control block which has the coagulation time detection section and is used for controlling the reagent or the reaction solution in the disposable reaction container to have a constant temperature; and a reagent dispensing syringe which is connected to the second reagent dispensing mechanism with a heating function; characterized by further including a fluid temperature control mechanism which is configured to control the temperature of an internal fluid of the reagent dispensing syringe by heating the fluid to a constant temperature and maintaining the temperature.