To provide a CW tone filter by which a tone scale of a CW tone signal or a side tone signal from a receiver is optionally changed.

An input signal is given to a band-pass filter 1, where a prescribed band limit is received and converted into two signals whose phase difference is 90° t a Hilbert filter 2 and and a delay circuit 3 and given respectively to 1st and 2nd multipliers 4, 5. On the other hand, a signal with a phase difference of 90° from an output signal of a low frequency oscillator 7 is fed to the 1st multiplier 4 and an output signal of the low frequency oscillator 7 is given to the 2nd multiplier 5 respectively, in which multiplication processing is conducted. The result of multiplication is added/subtracted by an adder/ subtractor 6, then a signal resulting from a frequency of the input signal changed by an oscillated frequency of the low frequency oscillator 7 is obtained.