[Object]To provide a portable terminal device accepting an input operation in accordance with acceleration, which is less prone to cause incorrect input and allows a user to perform easily an input operation.[Constitution]A mobile phone includes an acceleration sensor 13 for detecting acceleration produced on a mobile phone main body; a cumulative value calculating section 100a for calculating a cumulative value of detected acceleration; a comparing section 100b for comparing the cumulative value with a threshold value; and a CPU 100 for controlling a security lock mode in accordance with a result of comparison by the comparing section 100b. When the cumulative value has exceeded the threshold value by a user shaking the mobile phone, the CPU 100 cancels the security lock mode.