A main word line driving circuit for driving word lines in a memory device comprises first and second level shifting units and an inverting unit. The first level shifting unit is configured to convert a decode signal into a first operative signal, and the second level shifting unit is configured to convert the decode signal into a second operative signal. The inverting unit is configured to receive the first and second operative signals. A supply voltage of the first level shifting unit is selectively switched to a first bias voltage when the plurality of word lines are selected or partially selected and switched the output voltage to a second bias voltage when the plurality of word lines are deselected.