MEMORY DEVICE AND OPERATING METHOD OF THE MEMORY DEVICE

There are provided a memory device and an operating method of the memory device. The memory device includes: a memory block including first select transistors, memory cells, and second select transistors, which are connected between bit lines and a source line; a precharge controller for monitoring a program operation of the memory cells, and changing a precharge mode of unselected strings among strings included in the memory block according to a monitoring result; and a select line voltage generator for generating a positive voltage or a negative voltage, which is applied to a second select line connected to the second select transistors, according to the precharge mode selected in the precharge controller.