HYDRAULIC DRIVE SYSTEM FOR WORK VEHICLE

The aim of the present invention lies in providing a hydraulic drive system for a work vehicle, in which hydraulic oil can be supplied to an accumulator when a work device is raised, and in which, when the work device is held in a raised state, except during loaded travel, lowering of the work device caused by leakage of hydraulic oil inside a bottom chamber of a hydraulic cylinder into a hydraulic oil tank through a gap in a control valve can be reliably prevented. When a work device (2) is raised, discharge oil from a main pump (13) is conducted through an accumulator valve (61) to an accumulator (40). Further, when the work device (2) is held in a raised state, except during loaded travel, leakage of hydraulic oil inside a bottom chamber (11a) of a lift arm cylinder (11) into a hydraulic oil tank (17) through a gap in a control valve (20) for the lift arm is prevented by means of a poppet (71) of a load retention valve (70).