| 摘要 |
PROBLEM TO BE SOLVED: To provide a means for notifying a lifetime of a power failure power source to a user by use of a telephone set connected to a telephone exchanger about an exchange timing of the power-failure power source (battery) which is used for the telephone exchanger. SOLUTION: A central controller 307 monitors message display data 500 stored in a storage device 308 by use of clock information 310 and when it determined that a message is required to display, it extracts display data from the message display data 500 and displays the message in an internal line terminal 305.
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