A battery state estimation system which is configured to estimate a state of charge of a chargeable battery, said battery state estimation system comprising: an SOCv computing unit which is configured to calculate a state of charge of the battery using a voltage applied across the battery; an SOCi computing unit which is configured to integrate a current flowing through the battery to calculate a state of charge of the battery; and an SOCw computing unit which is configured to perform weighted addition to the state of charge of the battery calculated by the SOCv computing unit and the state of charge of the battery calculated by the SOCi computing unit; a temperature measuring unit which is configured to measure the temperature of the battery; a current measuring unit which is configured to measure the current flowing through the battery; a voltage measuring unit which is configured to measure the voltage applied across the battery; a resistance measuring unit which is configured to measure an internal resistance of the battery; and a weight computing unit which is configured to calculate a weight used when the SOCw computing unit performs the weighted addition, wherein the weight computing unit is configured to calculate the weight in such a manner that the weight related to the state of charge calculated by the SOCv computing unit becomes large as the current flowing through the battery becomes smaller, and the weight related to the state of charge calculated by the SOCv computing unit becomes large as the internal resistance of the battery becomes smaller; said battery state estimation system characterised by: a storage unit which is configured to store therein an association table in which a correlation between the temperature of the battery, the current flowing through the battery and a coefficient is defined, wherein when the temperature of the battery is a predetermined temperature threshold value or less and the current flowing through the battery is a predetermined current threshold value or less, the weight computing unit is configured to calculate the weight by referring to the association table with the temperature of the battery and the current flowing through the battery as keys and multiplying with an inverse of the coefficient to thereby decrease the weight related to the state of charge of the battery calculated by the SOCv computing unit and increase the weight related to the state of charge of the battery calculated by the SOCi computing unit, wherein the weight is corrected in such a manner that the weight related to the state of charge of the battery calculated by the SOCi computing unit is mainly used in cases when the battery current is small and the battery temperature is low. an SOCv computing unit which is configured to calculate a state of charge of the battery using a voltage applied across the battery; an SOCi computing unit which is configured to integrate a current flowing through the battery to calculate a state of charge of the battery; and an SOCw computing unit which is configured to perform weighted addition to the state of charge of the battery calculated by the SOCv computing unit and the state of charge of the battery calculated by the SOCi computing unit; a temperature measuring unit which is configured to measure the temperature of the battery; a current measuring unit which is configured to measure the current flowing through the battery; a voltage measuring unit which is configured to measure the voltage applied across the battery; a resistance measuring unit which is configured to measure an internal resistance of the battery; and a weight computing unit which is configured to calculate a weight used when the SOCw computing unit performs the weighted addition, wherein the weight computing unit is configured to calculate the weight in such a manner that the weight related to the state of charge calculated by the SOCv computing unit becomes large as the current flowing through the battery becomes smaller, and the weight related to the state of charge calculated by the SOCv computing unit becomes large as the internal resistance of the battery becomes smaller; said battery state estimation system characterised by: a storage unit which is configured to store therein an association table in which a correlation between the temperature of the battery, the current flowing through the battery and a coefficient is defined, wherein when the temperature of the battery is a predetermined temperature threshold value or less and the current flowing through the battery is a predetermined current threshold value or less, the weight computing unit is configured to calculate the weight by referring to the association table with the temperature of the battery and the current flowing through the battery as keys and multiplying with an inverse of the coefficient to thereby decrease the weight related to the state of charge of the battery calculated by the SOCv computing unit and increase the weight related to the state of charge of the battery calculated by the SOCi computing unit, wherein the weight is corrected in such a manner that the weight related to the state of charge of the battery calculated by the SOCi computing unit is mainly used in cases when the battery current is small and the battery temperature is low.