A memory device includes a word line driver circuit, which can advantageously reduce gate stress on a transistor using a lower high voltage that varies with a command, and an operating method of the memory device. The memory device includes a plurality of memory blocks, provides a high voltage or the lower high voltage to a variable high voltage line in response to a block select signal, and changes a level of the lower high voltage to a low voltage level, a medium voltage level, or a high voltage level based on the command. The memory device applies the lower high voltage to gates of P-type metal oxide semiconductor (PMOS) transistors connected to a word line driving signal, which drives word lines of non-selected memory blocks among the plurality of memory blocks.