An object of the invention is to achieve a travel speed known in the art during travelling operation, improve energy efficiency by reducing energy loss, and obtain favorable travel operability less susceptible to effects from variations in a travel load and changes in a pump delivery pressure when travelling operation is performed through operation of a travel lever over a half stroke range or less. A variable restrictor valve 80 is disposed in parallel with a flow sensing valve 50 of an engine speed sensing valve unit 13. A travel pilot pressure is adapted to act in an opening direction of the variable restrictor valve 80. The variable restrictor valve 80 is set to have a continuously increasing opening area from a full closure to a maximum with an increasing travel pilot pressure. Travel flow control valves 6d and 6e have an opening area that allows a predetermined flow rate QT required for traveling to be obtained even when a target LS differential pressure is decreased to a second specified value Pa3 when the travel lever is fully operated. In a first half of a spool stroke, the travel flow control valves 6d and 6e have an opening area approximate to an opening area of comparative example 1.