To provide a crawler unit whose handle steering power is small and the straight-line stability is good, and strand performance is fine.

As for an oscillating crawler unit, it has a fixed frame 2, an oscillating frame 4 supported in free oscillation around fulcrum 3 on the fixed frame 2, a sprocket 5 supported in free rotation on the fixed frame 2, a guided wheel 6 and rotary wheel 7 supported by rotation possible on the oscillating frame 4, a belt 9 wound to the sprocket 5, the guided wheel 6 and the rotary wheel 7, and a spring equipped between the fixed frame 2 or a member 18 fixed on the fixed frame 2 and the oscillating frame 4. It may be equipped with a stopper 30 on the fixed frame 2 or the oscillating frame 4. A spring 20 is equipped between the fixed frame 2 and a vehicle body or member on a vehicle body side.