An auto analyzer comprising: a cell disk configured to hold a cell along its circumference, the cell containing a reaction solution in which a sample and a reagent are mixed, the cell disk being configured to alternate between rotating and being stationary; and a light measuring unit configured to irradiate the cell with irradiating light from a light source while the cell disk is rotating, and to measure light that has interacted with the reaction solution in the cell, wherein the light measuring unit comprises: a first photoreceiver configured to receive scattering light (34a, 34,b) that is closer to an optical axis of the irradiating light; and a second photoreceiver configured to receive scattering light (34a, 34b) that is further from the optical axis, wherein changes in the amounts of light received by the photoreceivers over time are respectively measured as reaction process data, characterized by an analysis unit for determining a component amount in the reaction solution using data obtained by subtracting noise from the reaction process data of the first photoreceiver, the noise being estimated by multiplying a difference between the reaction process data of the second photoreceiver and a fitting function for fitting the reaction process data of the second photoreceiver by a sensitivity ratio between the first photoreceiver and the second photoreceiver. a cell disk configured to hold a cell along its circumference, the cell containing a reaction solution in which a sample and a reagent are mixed, the cell disk being configured to alternate between rotating and being stationary; and a light measuring unit configured to irradiate the cell with irradiating light from a light source while the cell disk is rotating, and to measure light that has interacted with the reaction solution in the cell, wherein the light measuring unit comprises: a first photoreceiver configured to receive scattering light (34a, 34,b) that is closer to an optical axis of the irradiating light; and a second photoreceiver configured to receive scattering light (34a, 34b) that is further from the optical axis, wherein changes in the amounts of light received by the photoreceivers over time are respectively measured as reaction process data, characterized by an analysis unit for determining a component amount in the reaction solution using data obtained by subtracting noise from the reaction process data of the first photoreceiver, the noise being estimated by multiplying a difference between the reaction process data of the second photoreceiver and a fitting function for fitting the reaction process data of the second photoreceiver by a sensitivity ratio between the first photoreceiver and the second photoreceiver. a first photoreceiver configured to receive scattering light (34a, 34,b) that is closer to an optical axis of the irradiating light; and a second photoreceiver configured to receive scattering light (34a, 34b) that is further from the optical axis, wherein changes in the amounts of light received by the photoreceivers over time are respectively measured as reaction process data, characterized by an analysis unit for determining a component amount in the reaction solution using data obtained by subtracting noise from the reaction process data of the first photoreceiver, the noise being estimated by multiplying a difference between the reaction process data of the second photoreceiver and a fitting function for fitting the reaction process data of the second photoreceiver by a sensitivity ratio between the first photoreceiver and the second photoreceiver.