A wideband transmitting and receiving apparatus including a local oscillator (LO) synthesizer providing a constant output to a wide band is provided. The LO synthesizer may generate LO signals of different amplitudes according to channels. The LO synthesizer may store the amplitudes of the LO signals different according to the channels and compensate the amplitudes of the LO signals using the stored amplitudes. Accordingly, the LO synthesizer may output the LO signals of uniform amplitudes irrespective of the channels.