PURPOSE: To obtain the generation probability of a wide range while keeping the circuit simple, by generating plural kinds of independent digital noise signals having different production probability and outputting the sum optionally so as to set the production probability of digital noise.

CONSTITUTION: An output of a proper position output of a PN series generator 6 is used as an input address 7 and each bit has an output corresponding to an independent and different production probability of digital noise by a ROM 8. Then noise generators 12a∼12i receive input from the output of the ROM 8 and use the selected and added sum of each input bit based on the noise generation probability set signal as the final digital noise output. Thus, the addition sum of the digital noise having independent and different probability is used as the digital noise output, then the production probability of the digital noise is minute and set over a wide range.