Echo preventing circuit includes first and second FIR filters. The outputs of the first and second FIR filters are converted into first and second analog signals. An input/output terminal outputs the first analog signal or receives a third analog signal. An AD converter converts an analog signal obtained by subtracting the second analog signal from a signal formed by combining the first analog signal and the third analog signal. A response signal acquiring unit acquires a first response signal from an output of the first FIR filter to an output of the AD converter. A filter coefficient setting unit sets the filter coefficients of the second FIR filter based on the first response signal and sets the filter coefficients of the first FIR filter based on second response signal of a section from and output of the second FIR filter to an output of the AD converter.