The present invention relates to a mobile device having a function of controlling a call connection in a lock mode by using a voice signal. The mobile device includes: a keypad 110 which allows a user to input an execution command for setting a specific function or for performing a specific function; a controller 130 which performs a corresponding operation in accordance with the execution command input to the keypad 110, a preset internal function, or an execution command applied from the outside; a microphone 140 which allow the user to input a voice command under the control of the controller 130; a memory 160 stores at least one preset reference command under the control of the controller 130 and stores the voice command input through the microphone 140 under the control of the controller 130; an LED 180 which represents an operation state of the mobile device under the control of the controller 130; a wireless transceiver 190 which performs a voice call or a data communication between a transmitting terminal and a receiving mobile device; and a speaker 195 which outputs a specific operation state or a user's voice signal under the control of the controller 130. When the receiving mobile device receives an incoming call from any transmitting terminal in a lock mode, the controller 130 converts automatically the mobile device into a voice input mode for a predetermined period of time, and when it is determined that a specific voice command input by the user of the receiving mobile device in the voice input mode is successfully recognized by the receiving mobile device, the controller 130 controls the wireless transceiver 190 to control a call connection between the transmitting terminal and the receiving mobile device.