Patent ID: 7895833

Claim:
A hydraulic drive system provided with a main hydraulic pump, a first hydraulic cylinder and second hydraulic cylinder driven by pressure oil delivered from said main hydraulic pump, a first directional control valve for controlling a flow of pressure oil to be fed from said main hydraulic pump to said first hydraulic cylinder, a second directional control valve for controlling a flow of pressure oil to be fed from said main hydraulic pump to said second hydraulic cylinder, a first control device for selectively controlling said first directional control valve, and a second control device for selectively controlling said second directional control valve, wherein: said hydraulic drive system is provided with a communication control means for communicating a rod chamber of said first hydraulic cylinder and a bottom chamber of said second hydraulic cylinder with each other irrespective of a level of pressure of a bottom chamber of said second hydraulic cylinder when a stroke of said second control device has increased to at least a predetermined amount.