A battery state estimation device for estimating a state of a battery system including a plurality of battery cells, the battery state estimation device comprising: a storage unit configured to store correspondence data that describes a correspondence among a time derivative of an output voltage during a pause period after discharge of the battery cell, a temperature of the battery cell during the pause period, and a deterioration state of the battery cell; and a calculation unit configured to calculate the deterioration state of the battery cell using the correspondence data, wherein the calculation unit is configured to acquire measurement data in which measurement results of output voltages and battery temperatures of the plurality of battery cells are described, wherein the battery state estimation device is characterised in that the calculation unit is configured to acquire a first output voltage of a first battery cell of the battery system and acquire a first temperature of the first battery cell from the measurement results described in the measurement data, the calculation unit is configured to acquire a second output voltage of a second battery cell of the battery system and acquire a second temperature of the second battery cell from the measurement results described in the measurement data, the calculation unit is configured to estimate a first deterioration state of the first battery cell by referring to the correspondence data using a time derivative of the first output voltage and the first temperature, the calculation unit is configured to estimate a second deterioration state of the second battery cell by referring to the correspondence data using a time derivative of the second output voltage and the second temperature, and the calculation unit is configured to obtain an evaluation parameter representing a deterioration state of the entire battery system by using the first deterioration state and the second deterioration state to estimate a deterioration state of the entire battery system. a storage unit configured to store correspondence data that describes a correspondence among a time derivative of an output voltage during a pause period after discharge of the battery cell, a temperature of the battery cell during the pause period, and a deterioration state of the battery cell; and a calculation unit configured to calculate the deterioration state of the battery cell using the correspondence data, wherein the calculation unit is configured to acquire measurement data in which measurement results of output voltages and battery temperatures of the plurality of battery cells are described, wherein the battery state estimation device is characterised in that the calculation unit is configured to acquire a first output voltage of a first battery cell of the battery system and acquire a first temperature of the first battery cell from the measurement results described in the measurement data, the calculation unit is configured to acquire a second output voltage of a second battery cell of the battery system and acquire a second temperature of the second battery cell from the measurement results described in the measurement data, the calculation unit is configured to estimate a first deterioration state of the first battery cell by referring to the correspondence data using a time derivative of the first output voltage and the first temperature, the calculation unit is configured to estimate a second deterioration state of the second battery cell by referring to the correspondence data using a time derivative of the second output voltage and the second temperature, and the calculation unit is configured to obtain an evaluation parameter representing a deterioration state of the entire battery system by using the first deterioration state and the second deterioration state to estimate a deterioration state of the entire battery system.