A hydraulic piping structure for controlling a boom assembly supported through a swing bracket by a swivel deck of a backhoe. The piping structure includes a plurality of hydraulic hoses for supplying oil from a pressure source mounted on the swivel deck to hydrauylic cylinders for controlling a boom and other components of the boom assembly. These hoses are arranged parallel on an upper face of the boom, with hoses connected to a boom cylinder being curved on a vertical plane. The parallel boses extend to the swivel deck through an interior space of the swing bracket and are fixed in position by a clamp mechanism therein. On the swivel deck, these hoses are separated into two batches and fixed in position by further clamp mechanisms, respectively.