1. An apparatus for determining a mental state of a user, comprising: a data collector configured to collect sensor data generated as the user is composing a message using a terminal; a mental state determiner configured to determine the mental state of the user based on extracted feature data from the sensor data; and a measure executor configured to control an implementation of one or more predetermined measures based on the determined mental state, wherein the feature data comprises text input information, and the text input information comprises one or more of keyboard input information, writing input information, and terminal state information.