An apparatus for generating a reference voltage of a semiconductor integrated circuit includes a resistance control unit that adjusts at least one an adjustment code such that at least one set of resistors, which have resistances determined according to the at least one adjustment code have predetermined resistances, a voltage level control unit that generates a selection code for selecting the level of a final reference voltage under external control and outputs the generated selection code, and a reference voltage generating unit that converts a power supply voltage according to the adjustment code and the selection code and outputs the final reference voltage.