An apparatus for estimating SOC for estimating a SOC of a vehicle-starting battery, comprising: a current measuring unit configured to measure a discharge current value of the battery; a voltage measuring unit configured to measure a terminal voltage value of the battery; a processor configured to receive the discharge current value, the terminal voltage value of the battery from the current measuring unit and the voltage measuring unit, and to measure a parking duration of the vehicle; wherein the processor is further configured to determine a SOC estimation mode based on the parking duration, and estimate an initial SOC of the battery at the starting of the vehicle based on the discharge current value during the parking duration according to the determined SOC estimation mode, or correct the terminal voltage value of the battery based on the discharge current value when measuring the terminal voltage of the battery and estimate the initial SOC of the battery at the starting of the vehicle based on the corrected terminal voltage value of the battery, characterised in that the SOC estimation mode includes a SOC correction mode in which the initial SOC of the battery at the starting of the vehicle is estimated based on the discharge current value of the battery during the parking duration, and an OCV estimation mode in which the terminal voltage value of the battery is corrected based on the discharge current value of the battery and the initial SOC of the battery at the starting of the vehicle is estimated based on the corrected terminal voltage value of the battery, and wherein the processor is configured to determine that the SOC estimation mode is the SOC correction mode when the parking duration is smaller than a predetermined reference time value and to determine that the SOC estimation mode is the OCV estimation mode when the parking duration is equal to or greater than the predetermined reference time value. a current measuring unit configured to measure a discharge current value of the battery; a voltage measuring unit configured to measure a terminal voltage value of the battery; a processor configured to receive the discharge current value, the terminal voltage value of the battery from the current measuring unit and the voltage measuring unit, and to measure a parking duration of the vehicle; wherein the processor is further configured to determine a SOC estimation mode based on the parking duration, and estimate an initial SOC of the battery at the starting of the vehicle based on the discharge current value during the parking duration according to the determined SOC estimation mode, or correct the terminal voltage value of the battery based on the discharge current value when measuring the terminal voltage of the battery and estimate the initial SOC of the battery at the starting of the vehicle based on the corrected terminal voltage value of the battery, characterised in that the SOC estimation mode includes a SOC correction mode in which the initial SOC of the battery at the starting of the vehicle is estimated based on the discharge current value of the battery during the parking duration, and an OCV estimation mode in which the terminal voltage value of the battery is corrected based on the discharge current value of the battery and the initial SOC of the battery at the starting of the vehicle is estimated based on the corrected terminal voltage value of the battery, and wherein the processor is configured to determine that the SOC estimation mode is the SOC correction mode when the parking duration is smaller than a predetermined reference time value and to determine that the SOC estimation mode is the OCV estimation mode when the parking duration is equal to or greater than the predetermined reference time value.