| 摘要 |
PURPOSE:To listen easily with an appropriate tone volume of a receiving tone by increasing/decreasing the amplification factor of a cariable amplifier circuit between a telephone receiver and a receiving part according to the sizes of noise that is detected by a sound receiving element. CONSTITUTION:A noise detecting part 7 detects an electrical signal which a sound receiving element 8 generates due to peripheral noise and sets the amplification factor of a variable amplifier circuit 15 that is provided between a telephone receiver and a receiving part 4 to lower when the peripheral noise is less. On the other hand, when the peripheral noise is greater, the detecting part 7 raises the amplification factor of the circuit 15. Thus, it is made possible to listen easily the receiving tone by the generation of the appropriate receiving tone corresponding to the peripheral noise.
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