A safety device for an elevator system, and an elevator system. The elevator system includes a guide rope arranged in a hoistway to be used as a guide rail and a running device running along the guide rope, and the safety device includes a body which is connected to the running device, and a first component and a second component which are provided on the body and define a passage for the guide rope to pass through freely when the running device is in normal operation, the first and second components are configured for clamping the guide rope in the passage when a running speed of the running device exceeds a threshold, to restrict the speed of the running device or stop the running device.