PROBLEM TO BE SOLVED: To increase the hit ratio of the conversion of a character input and security by detecting an accent in response to a series of depressions of keys in the character input, and adding the accent to a character string. SOLUTION: A vibration sensor 10 is mounted on a keyboard 1, and an electric signal corresponding to the vibration of the keyboard 1 generated at the time of key input is transmitted to an accent detecting part 5. A signal amplified by an amplifier 51 is inputted to a waveform processing part 52 equipped with a sample and hold circuit, and a peak value is extracted from a sample value, and held. A comparator circuit 53 receives the output Ko of the waveform processing part 52, and compares it with a preliminarily set reference level (ref), and when the output Ko is larger than the reference level (ref), an accent signal (acc) is outputted. When the accent signal (acc) is transmitted in almost the same timing as a character is received from a character string forming part 3, an accent adding part 4 adds a code indicating the presence of an accent as an attribute of the character.
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