To provide a lower traveling body that makes a translifter device light weight and inexpensive, even though a connection structure using a connection link, which excels in connection accuracy and facilitates an expanding and contracting work of a crawler width, is adopted.

This lower traveling body has such a configuration that the base end side of a connection link 7 of a connection device 4 is connected to a mounting bracket 6 provided on a truck frame 1, and that the fore end plunges into a linkage opening provided on a crawler frame. In addition, the connection link 7 is provided with a fore end stopper 7b, and also provided with a pin hole 7c for the expansion that, when an outer end surface 5ao of a bracket 5 for the expansion and contraction comes into contact with this fore end stopper 7b, matches with an upper pin hole 5b and a lower pin hole 5d thereof, and maintains the expansion position of the crawler width. Meanwhile, a base end stopper 7e is provided, and also a pin hole 7d for the contraction is provided that, when an inner end surface 5ai of the bracket 5 for the expansion and contraction comes into contact with this base end stopper 7e, matches with the upper pin hole 5b and the lower pin hole 5d thereof, and maintains the contraction position of the crawler width.