Safety device, self-propelled robot system, and controlling method

A safety device, comprising:

• a sensor that is attached to a self-propellable travel device or a robot provided to the travel device, is set with a given detection area on the basis of a position of the sensor, and detects an object existing within the given detection area;
• a motion suppressing device that suppresses motions of the travel device and the robot, when the existence of the object within the given detection area is detected by the sensor;
• and
• an area changing device that changes the given detection area according to operating states of the travel device and the robot, wherein
• the area changing device is changeable between:
• a first detection area as the given detection area extending from the travel device at least in a traveling direction of the travel device, when the robot does not operate and the travel device travels, and
• a second detection area as the given detection area extending from the robot at least toward a movable area where the robot is operable, when the travel device does not travel and the robot operates.