The storage device includes a storage unit configured to store data, an error controlling unit configured to correct an error of the data read out from the storage unit according to at least one read level, and a read level controlling unit configured to control the at least one read level when the error is uncorrectable. The read level controlling unit is configured to measure a distribution of memory cells of the storage unit, configured to filter the measured distribution, and configured to reset the at least one read level based on the filtered distribution.