Abstract: In the frequency conversion apparatus, the frequency of an analog signal is converted into optional frequency with a simple construction without requiring digital signal processing. The phase component of the input signal is phase shifted to the first and second phase-shifting signal having orthogonal phases, then the phase-shifted signals are multiplied by the first and second oscillating outputs having orthogonal phases and are modulated. Continuously, by multiplying the third oscillating output by a side-band signal extracted by adding the first and second multiplied outputs to each other. A third multiplied output can be obtained comprising the demodulated signal of the input signal. Thereby, the frequency of the input signal can be converted into any frequency by analog processing without performing digital signal processing.