PURPOSE: To make the random number generating probability almost uniform, by suppressing the generating time of a random number or the output of the random number to be converted to external part corresponding to the random number, when the generation of the random numer outside the objective range is detected.

CONSTITUTION: A clock signal CLK becomes a latch pulse LP via a frequency division circuit 1 and operated to an n-bit latch circuit 8 and to an n-bit ring counter 3 as a shift pulse via an OR gate 14. Thus, the random number sequentially revised is picked up as an external output EO via the circuit 8. In generating a random number in the range of integers K1WK2, a random number within the range of K2+1W2n-1 and 1WK1 controls an AND gate 13 via an OR gate 15 with the detected output of an excess random number detection circuit 4 and a deficient random number detection circuit 6 and the pulse SP is operated to the counter 3 before the next pulse LP is generated. Thus, the random number other than the objective number is not latched in the circuit 8, not picked up as the external output EO and the uniformity of the generating time and the number of times of the external output of the random number within a prescribed range can be obtained.