The present disclosure is directed to providing an SOC estimating apparatus and method, which may accurately estimate OCV and SOC of a battery cell even when a voltage rough graph of the battery cell exhibits a nonlinear rough graph. According to an aspect of the present disclosure, the SOC estimating apparatus has an advantage of estimating the SOC of the battery cell more accurately and more reliably. In addition, the SOC estimating apparatus has an advantage of estimating the final SOC of the battery cell quickly even in an environment where it is difficult to secure a sufficient rest period, by estimating the second SOC based on voltage information obtained during the charging and discharging interruption time.