Provided are a voltage control circuit including an assist circuit and a memory device including the voltage control circuit. The memory device includes: a volatile memory cell array, which is connected to a plurality of word lines and includes a memory cell including at least one transistor; and an assist circuit, which is connected to at least one of the plurality of word lines and adjusts a driving voltage level of each of the plurality of word lines, wherein the assist circuit includes a diode N-channel metal oxide semiconductor (NMOS) transistor having a gate and a drain connected to each other.