Embodiments of the present invention disclose a frequency divider and a radio communications device. The frequency divider includes a shift register unit and an output frequency synthesizing unit; the shift register unit includes multiple cyclically cascaded basic units; a basic unit at each level includes 2N D flip-flops connected in series and a multiplexer, outputs of the 2N D flip-flops connected in series are separately connected to the multiplexer; an output of the multiplexer is connected to an input of a next-level basic unit; the output frequency synthesizing unit superposes an output signal of the first D flip-flop of the basic unit at each level to generate a frequency division output signal.