A filtering circuit with a jammer generator cancels a jammer in wireless signals with little degradation of the signal-to-noise ratio (SNR). The filtering circuit may include a jammer generator which acquires information of period and phase of a sinusoidal jammer signal in a composite input sinusoidal signal, which includes the jammer signal and a desired signal, and outputs a pseudo sine-wave with a period and phase corresponding with the period and phase of the jammer signal acquired, and an adder which outputs a difference between the input and output signals of the jammer generator as the desired signal.