A first frequency dividing circuit and a second frequency dividing circuit are provided, and these circuits frequency-divide two-phase external clocks injected from an external part, to output four-phase clocks with phase guarantee. Each of the frequency dividing circuits includes a mixer, an adding circuit, and a phase circuit. The first frequency dividing circuit and the second frequency dividing circuit are coupled in loop shape via a first coupling circuit and a second coupling circuit. The first coupling circuit receives a first output signal of the first frequency dividing circuit to output a second external input signal to the second frequency dividing circuit, and the second coupling circuit receives a second output signal of the second frequency dividing circuit to output a first external input signal to the first frequency dividing circuit, and a clock frequency dividing circuit with a high loop gain and a wide lock range can be realized.