A filter device comprising: a filter circuit having a positive feedback therein; and a control circuit for controlling a center frequency of the filter circuit, wherein the control circuit sets the filter circuit in an oscillation state, while the center frequency is being controlled, wherein the filter circuit is a recursive filter circuit, wherein the recursive filter circuit comprises: an adder for outputting an added signal in which an input signal and a feedback signal are added; a variable gain amplifier for generating an amplification signal by amplifying the added signal output from the adder by a desired amplification factor; and a phase shifter for shifting a phase of the amplification signal amplified by the variable gain amplifier by any shift amount, generating the feedback signal, and inputting the feedback signal to the adder, wherein the control circuit comprises: a gain controller for generating a gain control signal of controlling the amplification factor of the variable gain amplifier in accordance with an amplitude of the feedback signal; and a phase controller for generating a phase shifter control signal of controlling a shift amount of the phase of the amplification signal in the phase shifter in accordance with a frequency of the feedback signal, characterized in that the gain controller comprises: an amplitude comparing circuit for comparing a reference amplitude that is an amplitude set as the reference and the amplitude of the feedback signal; and a gain control circuit for generating a gain control signal of controlling the amplification factor of the variable gain amplifier based upon a comparison result of the amplitude comparing circuit, and the phase controller comprises: a frequency comparing circuit for comparing the reference frequency that is the frequency set as the reference and the frequency of the feedback signal; and a phase control circuit for generating the phase shifter control signal of controlling the shift amount of the phase of the amplification signal in the phase shifter. a filter circuit having a positive feedback therein; and a control circuit for controlling a center frequency of the filter circuit, an adder for outputting an added signal in which an input signal and a feedback signal are added; a variable gain amplifier for generating an amplification signal by amplifying the added signal output from the adder by a desired amplification factor; and a phase shifter for shifting a phase of the amplification signal amplified by the variable gain amplifier by any shift amount, generating the feedback signal, and inputting the feedback signal to the adder, a gain controller for generating a gain control signal of controlling the amplification factor of the variable gain amplifier in accordance with an amplitude of the feedback signal; and a phase controller for generating a phase shifter control signal of controlling a shift amount of the phase of the amplification signal in the phase shifter in accordance with a frequency of the feedback signal, an amplitude comparing circuit for comparing a reference amplitude that is an amplitude set as the reference and the amplitude of the feedback signal; and a gain control circuit for generating a gain control signal of controlling the amplification factor of the variable gain amplifier based upon a comparison result of the amplitude comparing circuit, and a frequency comparing circuit for comparing the reference frequency that is the frequency set as the reference and the frequency of the feedback signal; and a phase control circuit for generating the phase shifter control signal of controlling the shift amount of the phase of the amplification signal in the phase shifter.