A robot system including a robot, a control unit, a sensor to detect a magnitude of force applied to the robot, a determination unit configured to determine, based on the magnitude of the detected force, whether there is application of an external force different from a load acting on the robot during a task performed by the robot, and a storage unit to store the magnitude of force detected by the sensor when the control unit executes at least one operation command when there is no application of the external force, in association with the operation command, where the determination unit determines, when the operation command is executed by the control unit, presence or absence of the external force based on the magnitude of force stored in the storage unit in association with the operation command and the magnitude of force detected by the sensor.