| 摘要 |
PROBLEM TO BE SOLVED: To avoid trouble on surrounding persons by providing a means that detects a change in a light receiving quantity to automatically vary the tone level of a call tone and that changes automatically the changed call tone volume into the original tone volume again when the telephone set is contained in an enclosed space to reduce the level of the call tone when the telephone set is picked out from the inside of a bag or the like. SOLUTION: When the user hears a call tone and picks out a telephone set 1 from a bag, an optical sensor 101 receives a surrounding light, converts it into a digital signal and it is given to a control section 103. The control section 103 discriminates whether or not a light receiving quantity is changed from an initial setting value based on the received digital signal. Furthermore, when the section 103 discriminates it that the telephone set 1 is picked out from the bag, the control section 103 gives a tone volume control signal to an electronic volume 104 to decrease the tone volume more than the initial level thereby reducing the tone volume of the call tone from a sounder 107. When the user contains again the telephone set in the bag and the increase/ decrease in the light receiving quantity is almost unchanged from the preset value, the call tone level is kept to the state of the initial level.
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