PURPOSE: To shorten the input time and to improve the operability with an input device by releasing a shift lock state in case a mode switch key is applied when the input device is used in a shift lock state.

CONSTITUTION: The pass of a shift lock state is stored and the state of a shift lock key is checked when an input mode switch key is applied. Then the shift lock state if set is released. When an alphameric input mode switch key is applied in a certain execution mode, it is checked whether or not the shift lock key state is released by a KANA (Japanese syllabary) input mode switch key in terms of the state set before input of the alphameric input mode switch key. If the shift lock state is released, the original shift lock state is reset.