A driver state monitoring (DSM) system includes: a sensing unit configured to sense biological information of a user of a vehicle； and a controller configured to: determine a drowsy state of the user based on the sensed biological information, determine a current condition of traffic, output information recommending rest based on the determined drowsy state of the user and the determined current condition of traffic, monitor the traffic and determine a rest state of the user； and output an alarm based on monitoring the traffic and the determined rest state of the user.
