An electronic device with a plurality of keys which correspond to a plurality of standard voltages respectively comprises a voltage generation module, a detection module, storage, an acquiring module, a comparison module, and an extraction module. The voltage generation module with an initial voltage decreases the initial voltage to the standard voltage corresponding to the pressed key. The detection module detects whether the current voltage of the voltage generation module is equal to the initial voltage. The storage stores the current voltage as a reference voltage when the current voltage is not equal to the initial voltage. The acquiring module acquires a current voltage of the voltage generation module after a predetermined time. The comparison module compares the acquired current voltage with the reference voltage. When the acquired current voltage is equal to the reference voltage, the extraction module executes an operation corresponding to the reference voltage.