An automatic analyzer according to the present invention is compact, mounting great number of reagents, having high processing ability. Reagent disks are arranged at inside and outside of a reaction disk. A reagent probe can inject a reagent into the position which is common position of both reagent disks. One of plural reagent probes approaches to one of reagent disks at one cycle. Plural reagent probes alternatively approach to the reagent disk. Therefore, the first reagents and the second reagents can be placed on both reagent disks. The mounting number of reagents can be increased without enlarging an analyzer. The cycle time can be shortened to make an automatic analyzer to have high processing ability.