A memory device includes a cell area in which a plurality of word lines, a plurality of bit lines, and a plurality of memory cells connected to the plurality of word lines and the plurality of bit lines are disposed, each of the plurality of memory cells including an Ovonic threshold switch element and a memory element connected to each other in series, and a peripheral circuit area including at least one peripheral circuit, configured to input a first refresh voltage turning on the Ovonic threshold switch element to each of at least some refresh cells among the plurality of memory cells to execute a refresh operation, determine each of the refresh cells as a first refresh cell in a first state or a second refresh cell in a second state while the Ovonic threshold switch element is turned on, and input a second refresh voltage, different to the first refresh voltage, to the second refresh cell.