Disclosed is an operation method of a memory device which includes floating a first driving line corresponding to a first word line from the first word line and precharging the first driving line with a first voltage, floating the first driving line from the first voltage to sense a first voltage variation of the first driving line, storing the first voltage variation in a first capacitor, electrically connecting the first driving line to the first word line and precharging the first driving line and the first word line with the first voltage, floating the first driving line and the first word line from the first voltage to sense a second voltage variation of the first driving line and the first word line, and outputting a first detection signal corresponding to a first leakage current through the first word line based on the first voltage variation and the second voltage variation.