1. A user authentication method comprising: receiving by a camera or a microphone of electronic device at least one of image information or voice information, respectively; identifying by a controller of the electronic device when only one of the at least one of image information and voice information has been received, whether another of the image information and voice information is received such that both image information and the voice information for authentication are received during a predetermined time period; detecting, if both image information and voice information are received within the predetermined time period, an object feature vector value based on the image information and a voice feature vector value based on the voice information; performing an integral user authentication for authentication by determining whether each of the detected feature vector values respectively matches with prestored information according to a respective user settable probability over a predetermined amount; determining, by a synchronization detection unit, whether the object feature vector value and the voice feature vector value are synchronized with each other, and outputting synchronization information; wherein when the synchronization information indicates that the object feature vector and the voice feature vector value are synchronized with each other, outputting information that the authentication is successful; wherein when the synchronization information indicates that the object feature vector and the voice feature vector are not synchronized with each other, outputting information that the authentication has failed; and outputting information indicating the user authentication has failed if the predetermined time period has elapsed and both image information and voice information have not been received.