An apparatus for estimating a state of a secondary battery, comprising: a charging unit electrically connectable to two terminals of the secondary battery to charge the secondary battery; a voltage measuring unit electrically connectable to the two terminals of the secondary battery to measure a voltage across the two terminals of the secondary battery; a time measuring unit configured to receive a voltage value of the secondary battery from the voltage measuring unit, and during charging of the secondary battery, in a predefined voltage range (V1-V2), to measure a charge time of the secondary battery corresponding to the voltage range sequentially at multiple times; and a control unit configured to transmit and receive an electrical signal to and from the charging unit, the voltage measuring unit and the time measuring unit, to calculate a ratio of a first charge time (a1, b1, c1) and a second charge time (a2, b2, c2) of the secondary battery measured by the time measuring unit sequentially, wherein a time interval passes in between sequential calculations of the ratio, and to estimate a state of the secondary battery, wherein the degradation level of the secondary battery is estimated according to the ratio of the first and the second charge time, based on the degradation level pre-stored in a memory unit; the memory unit being configured to pre-store the degradation level of the secondary battery corresponding to the ratio of the second charge time to the first charge time measured sequentially at multiple times; wherein the voltage range (V1-V2) includes a first voltage range in which a constant charge current is maintained, and a second voltage range in which a constant charge voltage is maintained, and the time measuring unit is configured to measure the charge time (a1+a2; b1+b2; c1+c2) of the secondary battery corresponding to each of the first voltage range and the second voltage range, which charge time corresponds to a range in which a constant charge current is maintained and, additionally, a range in which the charge time corresponds to the second voltage range in which a constant charge voltages is maintained; and wherein the control unit is configured to set a charge time (a1+a2) at the beginning of life of the secondary battery as the first charge time (a1+a2) and a charge time (b1+b2) measured at a time interval from the first charge time (a1+a2) as the second charge time (b1+b2), and calculate a ratio of the second charge time (b1+b2) to the first charge time (a1+a2). a charging unit electrically connectable to two terminals of the secondary battery to charge the secondary battery; a voltage measuring unit electrically connectable to the two terminals of the secondary battery to measure a voltage across the two terminals of the secondary battery; a time measuring unit configured to receive a voltage value of the secondary battery from the voltage measuring unit, and during charging of the secondary battery, in a predefined voltage range (V1-V2), to measure a charge time of the secondary battery corresponding to the voltage range sequentially at multiple times; and a control unit configured to transmit and receive an electrical signal to and from the charging unit, the voltage measuring unit and the time measuring unit, to calculate a ratio of a first charge time (a1, b1, c1) and a second charge time (a2, b2, c2) of the secondary battery measured by the time measuring unit sequentially, wherein a time interval passes in between sequential calculations of the ratio, and to estimate a state of the secondary battery, wherein the degradation level of the secondary battery is estimated according to the ratio of the first and the second charge time, based on the degradation level pre-stored in a memory unit; the memory unit being configured to pre-store the degradation level of the secondary battery corresponding to the ratio of the second charge time to the first charge time measured sequentially at multiple times; wherein the voltage range (V1-V2) includes a first voltage range in which a constant charge current is maintained, and a second voltage range in which a constant charge voltage is maintained, and the time measuring unit is configured to measure the charge time (a1+a2; b1+b2; c1+c2) of the secondary battery corresponding to each of the first voltage range and the second voltage range, which charge time corresponds to a range in which a constant charge current is maintained and, additionally, a range in which the charge time corresponds to the second voltage range in which a constant charge voltages is maintained; and wherein the control unit is configured to set a charge time (a1+a2) at the beginning of life of the secondary battery as the first charge time (a1+a2) and a charge time (b1+b2) measured at a time interval from the first charge time (a1+a2) as the second charge time (b1+b2), and calculate a ratio of the second charge time (b1+b2) to the first charge time (a1+a2).