Problem:To accurately detect the state of charge of a secondary battery regardless of the state of the same.Resolution Means:A secondary battery state detection device 1 for detecting the state of a secondary battery 14 has a measurement unit (voltage sensor 11) for measuring or estimating the open-circuit voltage of the secondary battery, a determination unit (control unit 10) for determining a state of charge by applying the open-circuit voltage measured or estimated by the measurement unit to a correlation equation expressing the relationship between the open-circuit voltage and state of charge, a calculation unit (control unit 10) for calculating a state of charge on the basis of the internal resistance of the secondary battery, and a correction unit (control unit 10) for correcting the correlation equation of the determination unit if the values of the state of charge determined by the determination unit and the state of charge calculated by the calculation unit differ.