A sub-harmonic frequency conversion device includes: a voltage controlled oscillator for generating first to eighth oscillation frequency (LO) signals having a constant phase difference; a first mixer for performing a switching operation to mix the first to fourth LO signals having a phase difference of 90° and input signals, and outputting first IF signals; and a second mixer for performing a switching operation to mix the fifth to eighth LO signals having a phase difference of 90° and the input signals, and outputting second IF signals. Accordingly, the sub-harmonic frequency conversion device can use the low-frequency LO signal, and the power consumption can be reduced. In addition, because the mixers are implemented using a symmetric structure of the MOS transistors, the circuit configuration can be easily implemented.