A battery management apparatus for calibrating a state of charge of a lithium iron phosphate battery, the battery management apparatus comprising: a voltage measuring unit configured to measure a voltage of the LFP battery and output a voltage value indicative of the measured voltage; a current measuring unit configured to measure a current of the LFP battery and output a current value indicative of the measured current; and a control unit configured to individually receive the voltage value and the current value and determine the SOC of the LFP battery based on results of integrating the current value over time, characterized in that the control unit is configured to enter a calibration mode when the determined SOC reaches a preset threshold SOC lower than a preset reference SOC, and while the control unit is operating in the calibration mode, the control unit is further configured to: calculate an average voltage value of voltage values received from the voltage measuring unit for a predefined time, calculate an average current value of current values received from the current measuring unit for the predefined time, calculate an average internal resistance value of the LFP battery for the predefined time based on the average voltage value and the average current value, determine if the average internal resistance value is equal to or larger than a preset reference resistance value, and when the average internal resistance value is equal to or larger than the reference resistance value, calibrate the determined SOC to the preset reference SOC, wherein the control unit is configured to calculate the average internal resistance value using the following Equation 1: R ave = V ave − OCV ref I ave in which in the Equation 1, V ave is the average voltage value, I ave is the average current value, OCV ref is a preset reference open circuit voltage value, R ave is the average internal resistance value, and the reference OCV value is a value indicative of an OCV of the LFP battery when the SOC of the LFP battery is equal to the reference SOC. a voltage measuring unit configured to measure a voltage of the LFP battery and output a voltage value indicative of the measured voltage; a current measuring unit configured to measure a current of the LFP battery and output a current value indicative of the measured current; and a control unit configured to individually receive the voltage value and the current value and determine the SOC of the LFP battery based on results of integrating the current value over time, characterized in that the control unit is configured to enter a calibration mode when the determined SOC reaches a preset threshold SOC lower than a preset reference SOC, and while the control unit is operating in the calibration mode, the control unit is further configured to: calculate an average voltage value of voltage values received from the voltage measuring unit for a predefined time, calculate an average current value of current values received from the current measuring unit for the predefined time, calculate an average internal resistance value of the LFP battery for the predefined time based on the average voltage value and the average current value, determine if the average internal resistance value is equal to or larger than a preset reference resistance value, and when the average internal resistance value is equal to or larger than the reference resistance value, calibrate the determined SOC to the preset reference SOC, wherein the control unit is configured to calculate the average internal resistance value using the following Equation 1: R ave = V ave − OCV ref I ave in which in the Equation 1, V ave is the average voltage value, I ave is the average current value, OCV ref is a preset reference open circuit voltage value, R ave is the average internal resistance value, and the reference OCV value is a value indicative of an OCV of the LFP battery when the SOC of the LFP battery is equal to the reference SOC. calculate an average voltage value of voltage values received from the voltage measuring unit for a predefined time, calculate an average current value of current values received from the current measuring unit for the predefined time, calculate an average internal resistance value of the LFP battery for the predefined time based on the average voltage value and the average current value, determine if the average internal resistance value is equal to or larger than a preset reference resistance value, and when the average internal resistance value is equal to or larger than the reference resistance value, calibrate the determined SOC to the preset reference SOC, wherein the control unit is configured to calculate the average internal resistance value using the following Equation 1: R ave = V ave − OCV ref I ave in which in the Equation 1, V ave is the average voltage value, I ave is the average current value, OCV ref is a preset reference open circuit voltage value, R ave is the average internal resistance value, and the reference OCV value is a value indicative of an OCV of the LFP battery when the SOC of the LFP battery is equal to the reference SOC. in which in the Equation 1, V ave is the average voltage value, I ave is the average current value, OCV ref is a preset reference open circuit voltage value, R ave is the average internal resistance value, and the reference OCV value is a value indicative of an OCV of the LFP battery when the SOC of the LFP battery is equal to the reference SOC.