A monitor system for a robot that includes a base installed on an installation surface, and a movable part supported movably with respect to the base, the monitor system including: a sensor that monitors the presence or absence of an object around the robot; and a monitored region control part that controls a monitored region of the sensor based on a motion command signal for the robot. The sensor has the monitored region on each of both sides across a vertical plane that includes a central axis line of the movable parts, and the monitored region control part makes the monitored region at the rear in a moving direction of the movable part smaller than the monitored region at the front in the moving direction of the movable part.