A driver state monitoring (DSM) system is configured to interact with a vehicle. The DSM system includes: a wearable device main body configured to be worn by a user; a display unit; an information collection unit configured to collect information related to a body state of the user; and a controller configured to: sense a situation associated with the user's body state based on the collected information; convert the collected information related to the body state of the user into a numerical value that represents the body state of the user in context of the sensed situation, based on pre-stored information for the sensed situation; calculate a well driving score for the user based on the numerical value that represents the body state of the user in context of the sensed situation, and control at least one of the display unit or an image information output device to display the well-driving score and the numerical value that represents the body state of the user in context of the sensed situation.