PURPOSE: To inexpensively obtain a two mode frequency-divider which is stable up to a high frequency by providing two fixed frequency-dividers different in frequency-dividing values in the two mode frequency-divider and switching the output by means of a control input so as to use it.

CONSTITUTION: Different frequencies f0 and f0' are given to two inputs of a switch 37. Here, the set points of counters 1 and 2 are assumed to be (a) and (b). The switch 37 is controlled by the carrier output of first counter 1 and the output of second counter 2 is assumed to be an output signal, whereby two counters 1 and 2 are reset by the output. Consequently, an output frequency which is obtained in a terminal 12 shows f0=fi/(ap+b) with respect to an input signal frequency fi. Since a frequency-dividing value shown in the denominator of an expression is a primary function in which parameters are set to be (a) and (b), the output frequency of the optical frequency-dividing value can be obtained.