A step-up/step-down circuit can be simplified as compared with conventional circuits by including a step-down unit for receiving a system clock pulse alternately providing a reference voltage (GND) and a system voltage V.sub.DD in a repeated manner to output a voltage V.sub.4 lower than the reference voltage (GND) by using a potential difference between the reference voltage (GND) and the system voltage V.sub.DD, a level shift unit for receiving the system clock pulse and the voltage V.sub.4 output from the step-down unit to output a pulse signal V.sub.o having a greater potential difference than the potential difference between the reference voltage (GND) and the system voltage VDD, and a step-up unit for receiving the pulse signal V.sub.o output from the level shift unit to output a voltage V.sub.7 higher than the reference voltage (GND).