A random number generating device of the present disclosure includes: an arithmetic random number generator that generates an arithmetic random number sequence; an arithmetic random number converter that sequentially reads at least one arithmetic random number from the arithmetic random number sequence and converts a value of the read arithmetic random number into a voltage or current value of at least two predetermined levels of gray scale having an identical polarity; a hysteresis unit that outputs values depending on a presently-input voltage or current value and a previously-input voltage or current value with respect to the sequentially-input voltage or current value; and a threshold processor that binarizes the output of the hysteresis unit.