Abstract: An automatic tuning apparatus for a filter includes a mode wherein a switching part is controlled so that a reference signal is inputted to the filter, a plural number of control signals are successively input to a control terminal of the filter, a tentative value of the control signal is determined based on respective amplitudes detected by an amplitude detection part as a “coarse tuning step”, a plural number of control signals are successively input in the vicinity of the tentatively determined value to a control terminal, and the value of the control signal is determined to be used in a mode as a “fine tuning step” based on respective phase differences detected by a phase comparator part”.

Abstract: Purposes to offer an automatic tuning apparatus for filter which enables an accurate tuning to be attained and is small size and low power consumption and a communication instrument using the above.