Hydraulic shovel

A line is provided with a line communicating the line and a hydraulic oil tank . The line is provided with a throttle to construct a throttle-provided line . When air is trapped between the hydraulic oil tank and the hydraulic pump , the hydraulic pump is driven to discharge the air from the throttle-provided line to the hydraulic oil tank , thereby removing the air in the hydraulic circuit . When the air is removed, resistance caused by the throttle is increased, which makes hydraulic oil flow from a pilot pump to a PPC valve. Since the throttle-provided line realizes air removal with a simple structure, a hydraulic cylinder can be supplied with the air-removed hydraulic oil from an initial stage, thereby enhancing responsiveness of the hydraulic cylinder