An automatic analyzer is capable of performing a preparation process on a reagent used to measure a highly urgent test item even during analysis operation, and is configured as follows. If there is no parameter for the analysis item regarding a new reagent, the parameters are downloaded. If the priority of reagent preparation is “high,” a sample pipetting scheduling process is temporarily stopped. If the priority of reagent preparation is not “high,” it is determined whether a waiting time limit has been exceeded, and if it has, the sample pipetting scheduling process is stopped temporarily, reagent preparation scheduling is performed, and the sample pipetting scheduling process is resumed. If it is determined that the waiting time limit has not been exceeded, if the priority of reagent preparation is “medium,” and if the reagent preparation mechanism is found available, then reagent preparation scheduling is performed.