To provide a hydraulic circuit of a loading work vehicle capable of replenishing optimum oil quantity in a hydraulic circuit for working machine at the time of an unloading, securing required hydraulic torque without changing engine torque and thereby increasing excess torque.

In a hydraulic circuit of a loading work vehicle having a hydraulic circuit for working machine 10 driving hydraulic transmission of a working machine by receiving discharge oil quantity Qw of a hydraulic pump for working machine 30, a steering hydraulic circuit 20 driving the hydraulic transmission of a steering by receiving discharge oil quantity Qst of a hydraulic pump for steering 40 and a flow dividing valve 60 switching and supplying discharge oil quantity Qs of an auxiliary hydraulic pump to either one between both of the hydraulic circuits 10 and 20, giving priority to the hydraulic circuit for steering 20, a variable displacement auxiliary hydraulic pump 50 A in which the higher working hydraulic pressure Pw becomes, the smaller displacement Vs becomes, is provided when working hydraulic pressure Pw exceeds prescribed hydraulic pressure Pu (Pw>Pu) by receiving working hydraulic pressure Pw of the hydraulic circuit 10 for working machine.