An automatic analyzer having no limitation on a range of a placeable position on a sample placement disk for patient specimens, emergency specimens, quality control samples, and calibration samples, and being capable of performing analysis while changing the number of simultaneously-measurable samples for each type of each specimen is provided. In the automatic analyzer, either a calibration sample dedicated disk or a patient specimen dedicated disk is placed in an analyzing unit 8 as a sample placement disk 19, and the analyzing unit 8 has a disk identifying unit 24 which identifies a type of the sample placement disk 19, and a computer 22 identifies the type of the sample placement disk 19 based on an identification result of the disk identifying unit 24, and performs analysis on a liquid sample based on the identified type of the sample placement disk 19.