A robot system including a robot arm driven by a servo motor; and a robot controller controlling an operation of the robot arm. The robot system further comprises a first detection section detecting a rotation amount of the servo motor; a second detection section attached to a tip portion of the robot arm, and detecting a velocity or acceleration of the tip portion of the robot arm; a computation section computing the velocity or acceleration of the tip portion of the robot arm based on values detected by the first detection section, and computing a deviation between this computed velocity or acceleration and the velocity or acceleration detected by the second detection section; and an emergency stop section for bringing the servo motor to an emergency stop when a magnitude of the deviation computed by the computation section is greater than a reference value.