A work vehicle comprising: a power transmission device configured to transmit rotation power from an engine to drive wheels (2, 3), the power transmission device comprising a plurality of hydraulic main speed change clutches (B1, B2) including a first-speed clutch, a second-speed clutch, a third-speed clutch and a fourth-speed clutch for a plurality of speed change stages (16a, 16b, 16c, 16d), and a hydraulic Hi-Lo clutch having a high speed clutch and a low speed clutch and capable of changing a speed at a high speed stage or a low speed stage, and configured to transmit power via the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch; control valves (195, 196, 207, 208) configured to adjust pressed states of the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch, and a speed change control device configured to control and change a vehicle speed in a multi-stage manner by the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch, wherein in a shift-up operation for changing a speed from a low speed stage range in which the low speed clutch is used to a high speed stage range in which the high speed clutch is used, the speed change control device is configured to decrease a pressure of the low speed clutch while keeping a pressure of the high speed clutch at a first pressure (Pa) higher than the pressure of the low speed clutch and keeping a pressure of the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), which is a speed change source, to transmit power by a combination of the high speed clutch and the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), and then to decrease the pressure of the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), while increasing the pressure of the high speed clutch, which has been kept at the first pressure (Pa) and increasing the pressure of the first-speed clutch of the plurality of hydraulic main speed change clutches (B1 and B2), which is a speed change destination. a power transmission device configured to transmit rotation power from an engine to drive wheels (2, 3), the power transmission device comprising a plurality of hydraulic main speed change clutches (B1, B2) including a first-speed clutch, a second-speed clutch, a third-speed clutch and a fourth-speed clutch for a plurality of speed change stages (16a, 16b, 16c, 16d), and a hydraulic Hi-Lo clutch having a high speed clutch and a low speed clutch and capable of changing a speed at a high speed stage or a low speed stage, and configured to transmit power via the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch; control valves (195, 196, 207, 208) configured to adjust pressed states of the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch, and a speed change control device configured to control and change a vehicle speed in a multi-stage manner by the plurality of hydraulic main speed change clutches (B1, B2) and the Hi-Lo clutch, wherein in a shift-up operation for changing a speed from a low speed stage range in which the low speed clutch is used to a high speed stage range in which the high speed clutch is used, the speed change control device is configured to decrease a pressure of the low speed clutch while keeping a pressure of the high speed clutch at a first pressure (Pa) higher than the pressure of the low speed clutch and keeping a pressure of the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), which is a speed change source, to transmit power by a combination of the high speed clutch and the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), and then to decrease the pressure of the fourth-speed clutch of the plurality of hydraulic main speed change clutches (B1, B2), while increasing the pressure of the high speed clutch, which has been kept at the first pressure (Pa) and increasing the pressure of the first-speed clutch of the plurality of hydraulic main speed change clutches (B1 and B2), which is a speed change destination.