Abstract: A working machine for use in a working system in which a pair of working machines, which are capable of traveling both on land and on a riverbed or the like, are respectively used for excavating gravel or the like on the bottom of the water and for transporting the same. The working machine is basically constructed such that an upper structure including an operator's cabin is mounted on a lower structure having a self-traveling mechanism, such as endless tracks, in such a manner that the heightwise position of the upper structure can be varied. The working machine is applied to a dredging machine for a shallow water area having an excavating mechanism juxtaposed in the vicinity of its upper structure, and to a transporting machine for a shallow water area having a load-carrying platform juxtaposed in the vicinity of its upper structure.