A random number generating method for an electronic device including a plurality of unit circuits each first and second logic circuits, each logic circuit having a same shape and being formed through a same fabrication process, and an amplifier circuit for forming a binary signal by amplifying a noise superposed on the differential voltage of threshold voltages of the first and the second logic circuits; and a signal variation detecting circuit for forming an output signal in response to a variation in any of a plurality of binary signals outputted from the plurality of unit circuits, wherein a plurality of binary signals outputted from the signal variation detecting circuit are combined to generate a random number.