An endoscope has a head assembly for entry in a body cavity. A guide apparatus for propulsion of the head assembly is provided, and includes a shaft sleeve, a support sleeve, a drive sleeve, drive gears, an endless track device, two intermediate gears, and a motor. Two wire devices are disposed to extend in an axial direction, have distal ends to which the intermediate gears are respectively secured, for transmitting rotation of the motor to the intermediate gears. In fail-safe control, if one of the wire devices is broken, the broken wire device is detected. When the broken wire device is detected, a limited mode is set for driving the endless track device with a normal one of the wire devices in limited performance relative to normal operation. In a preferred embodiment, the guide apparatus has a differential device and two brake devices.
