A capacity estimating apparatus for a secondary battery, comprising: a current-detecting section configured to detect a value of current flowing in the secondary battery; a voltage-detecting section configured to detect a voltage value of the secondary battery; a first estimating section configured to calculate a first estimate value (SOC I) of a remaining capacity of the secondary battery on the basis of an accumulated value of the current values detected by the current-detecting section; and a second estimating section configured to calculate a second estimate value (SOC OCV) of the remaining capacity of the secondary battery on the basis of the voltage value detected by the voltage-detecting section, wherein the first estimating section is configured to calculate a difference between the first estimate value (SOC I) and the second estimate value (SOC OCV), and to correct the first estimate value (SOC I) by correcting the accumulated value so as to gradually reduce the difference, characterized in that the first estimating section is configured to correct the first estimate value (SOC I) by multiplying the accumulated value by a first constant (k) larger than 0 and smaller than 1, when the first estimate value (SOC I) is lower than the second estimate value (SOC OCV) during a discharging state of the secondary battery or when the first estimate value (SOC I) is higher than the second estimate value (SOC OCV) during a charging state of the secondary battery, wherein the first estimating section is configured to correct the first estimate value (SOC I) by multiplying the accumulated value by a second constant (k) larger than 1, when the first estimate value (SOC I) is lower than the second estimate value (SOC OCV) during the charging state of the secondary battery or when the first estimate value (SOC I) is higher than the second estimate value (SOC OCV) during the discharging state of the secondary battery. a current-detecting section configured to detect a value of current flowing in the secondary battery; a voltage-detecting section configured to detect a voltage value of the secondary battery; a first estimating section configured to calculate a first estimate value (SOC I) of a remaining capacity of the secondary battery on the basis of an accumulated value of the current values detected by the current-detecting section; and a second estimating section configured to calculate a second estimate value (SOC OCV) of the remaining capacity of the secondary battery on the basis of the voltage value detected by the voltage-detecting section, wherein the first estimating section is configured to calculate a difference between the first estimate value (SOC I) and the second estimate value (SOC OCV), and to correct the first estimate value (SOC I) by correcting the accumulated value so as to gradually reduce the difference, to calculate a difference between the first estimate value (SOC I) and the second estimate value (SOC OCV), and to correct the first estimate value (SOC I) by correcting the accumulated value so as to gradually reduce the difference, characterized in that the first estimating section is configured to correct the first estimate value (SOC I) by multiplying the accumulated value by a first constant (k) larger than 0 and smaller than 1, when the first estimate value (SOC I) is lower than the second estimate value (SOC OCV) during a discharging state of the secondary battery or when the first estimate value (SOC I) is higher than the second estimate value (SOC OCV) during a charging state of the secondary battery, wherein the first estimating section is configured to correct the first estimate value (SOC I) by multiplying the accumulated value by a second constant (k) larger than 1, when the first estimate value (SOC I) is lower than the second estimate value (SOC OCV) during the charging state of the secondary battery or when the first estimate value (SOC I) is higher than the second estimate value (SOC OCV) during the discharging state of the secondary battery.