When tuning control of a receiver is started, a differential encoding section (6) calculates the phase difference by using phase detection data inputted from a discrete Fourier transform section (5), a fluctuation detecting section (11) converts a phase difference received from a differential encoding section (13) into a phase error, and a judgment section (12) judges whether a fluctuation is present or not. A correction control variable (e.g. π/2) is specified and sent to an oscillator control section (8) when a fluctuation is judged to be present, otherwise correction control is not ordered. Tuning control is ended when the oscillator control section (8) varies the control variable according to the order of correction control from the fluctuation detecting section (11).