According to one embodiment, an automatic analyzer includes a magnetic field generator, a photometric unit, a measurement unit, and a decision unit. The magnetic field generator causes magnetic separation in a reaction liquid stored in a cuvette by magnetic particles. The photometric unit includes a light source unit configured to generate light, and a detection unit configured to detect the light generated by the light source unit and generate an output signal corresponding to the detected light. The measurement unit measures a measurement item based on the output signal. The decision unit decides the use range of the output signal to be used to measure the measurement item in accordance with spatial unevenness of the magnetic separation by the magnetic field generator.
