A lock control technique suitable for voice communication terminals. A voice communication terminal includes an unattended state detecting unit which detects an unattended state of the terminal, when its user leaves the terminal, and a lock control unit. The lock control unit determines whether the unattended state detected by the unattended state detecting unit has continued for a given time period or longer. If determining that the unattended state has continued for the given time period or longer, the lock control unit controls the terminal's communication so that voice input to the terminal will not be transmitted to other parties in conversation and voice of any other party will not be output from the computer.