PURPOSE: To reset a shift register automatically to an original loop by revising the counting state of the cyclic shift register in response to the detected output of the cyclic shift register reaching a specific point state.

CONSTITUTION: The cyclic shift register is constituted of plural D flip-flops(D- FF) 1-5 connected in cascade. A detection circuit 18 detecting that the cyclic shift register reaches a specific point state is provided and the counting state of the cyclic shift register is revised in response to the detection output of the detection circuit 18. Thus, even when the cyclic shift register to generate a random number enters a singular point, a random number generator returned immediately to original cyclic loop is obtained.