Disclosed is an apparatus in a diversity system of a mobile terminal having a main receiving unit and a sub-receiving unit, which includes a sub-antenna for receiving an input signal and a part of a transmitted signal of a transmitting unit, a band-pass filter (BPF) designed to greatly attenuate a low-band frequency of the part of the transmitted signal received through the sub-antenna, a high-pass filter (HPF) for additionally attenuating the part of the transmitted signal attenuated through the BPF, a low-noise amplifier for minimizing a noise of an output value of the HPF, an HPF for passing therethrough only a high-frequency component of an output value of the low-noise amplifier, and a mixer for mixing output values of the HPF and outputting a baseband signal. One of two BPFs in the sub-receiving unit is replaced by one HPF, and thus the HPF can be fabricated on chip with the terminal receiving unit. Additionally, through the on-chip HPF, the use of an additional BPF is eliminated, and the size and the unit price of production of the mobile terminal can also be reduced.