A memory device may include: a memory region including a plurality of word lines, a self-refresh command generation circuit suitable for generating self-refresh commands for each predetermined interval during a self-refresh period, a refresh check circuit suitable for generating a ratio signal by checking a ratio which word lines refreshed in response to the self-refresh commands occupy among the plurality of word lines, a ratio adjustment circuit suitable for adjusting, among a plurality of auto-refresh commands inputted from an external device during an auto-refresh period, a ratio of to-be-applied commands, which are to be used for a refresh operation, to to-be-skipped commands, which are to be skipped for the refresh operation, according to the ratio signal, and a refresh operation circuit suitable for performing the refresh operation on the plurality of word lines in response to the self-refresh commands and the to-be-applied commands.