| 摘要 |
PROBLEM TO BE SOLVED: To provide a portable telephone system in which the operation time of a built-in battery is made longer by lighting up only the backlight of a needed part in accordance with an application to be operated. SOLUTION: When any application is made operable, a controlling part indexes a table stored in a memory and defining the validity/invalidity of the operation key corresponding to the application. When any of the operation keys of the operating part is operated (step 31), the backlight lighting is started (step 32). The controlling part detects which operation key of the operating part is operated again before lighting time set by the timer of the controlling part elapses and decides whether it is a valid key (step 33). In the case of the valid key, a first backlight 24 illuminating the nearest adjacent part of the valid key and a second backlight 24 for illuminating a displaying part are continuously lighted up (step 34) until the lighting time set by the timer of the controlling part elapses. |
