An internal voltage generator of a semiconductor memory device is capable of changing driving abilities between standby and active modes, to respond faster in the active mode and prevent a leakage current in the standby mode. The internal voltage generator of a semiconductor memory device comprises a driving controller for generating drive control signals having information about standby and active modes, a first voltage generator enabled by the drive control signals for comparing an internal voltage with a reference voltage in the standby and active modes, a first driver for generating the internal voltage according to a comparison performed by the first voltage generator, a second voltage generator enabled by the drive control signal for comparing the internal voltage with the reference voltage in the active mode, and a second driver for generating the internal voltage according to a comparison performed by the second voltage generator.