A work vehicle comprising: an engine installed in a traveling machine body supported by a traveling unit; and a transmission case incorporating a hydraulic continuously variable transmission configured to shift driving force from the engine, wherein the transmission case incorporates a forward/backward traveling switching mechanism configured to switch an output from the hydraulic continuously variable transmission between normal rotation and reverse rotation directions, wherein the engine is installed in a front portion of a frame member forming the traveling machine body, wherein the transmission case is coupled to a rear portion of the frame member, wherein the engine and the transmission case are coupled to each other in a driving-force transmittable manner via a driving force transmission shaft, wherein the work vehicle further comprises: a forward traveling valve for a forward traveling hydraulic clutch (537, 539) configured to enable and disable a normal rotation output transmitted toward the traveling unit; a backward traveling valve for a backward traveling hydraulic clutch configured to enable and disable a reverse rotation output transmitted toward the traveling unit; and a master valve configured to control hydraulic oil supplying to the forward traveling valve and the backward traveling valve, characterized in that a part of a hydraulic circuit establishing connection between the hydraulic pressure source and the hydraulic clutches is formed on a front lid member that is detachably attached to close a front surface opening of the transmission case, and wherein the forward traveling valve, the backward traveling valve, and the master valve are attached on a front surface side of the front lid member. an engine installed in a traveling machine body supported by a traveling unit; and a transmission case incorporating a hydraulic continuously variable transmission configured to shift driving force from the engine, wherein the transmission case incorporates a forward/backward traveling switching mechanism configured to switch an output from the hydraulic continuously variable transmission between normal rotation and reverse rotation directions, wherein the engine is installed in a front portion of a frame member forming the traveling machine body, wherein the transmission case is coupled to a rear portion of the frame member, wherein the engine and the transmission case are coupled to each other in a driving-force transmittable manner via a driving force transmission shaft, wherein the work vehicle further comprises: a forward traveling valve for a forward traveling hydraulic clutch (537, 539) configured to enable and disable a normal rotation output transmitted toward the traveling unit; a backward traveling valve for a backward traveling hydraulic clutch configured to enable and disable a reverse rotation output transmitted toward the traveling unit; and a master valve configured to control hydraulic oil supplying to the forward traveling valve and the backward traveling valve, characterized in that a part of a hydraulic circuit establishing connection between the hydraulic pressure source and the hydraulic clutches is formed on a front lid member that is detachably attached to close a front surface opening of the transmission case, and wherein the forward traveling valve, the backward traveling valve, and the master valve are attached on a front surface side of the front lid member. a forward traveling valve for a forward traveling hydraulic clutch (537, 539) configured to enable and disable a normal rotation output transmitted toward the traveling unit; a backward traveling valve for a backward traveling hydraulic clutch configured to enable and disable a reverse rotation output transmitted toward the traveling unit; and a master valve configured to control hydraulic oil supplying to the forward traveling valve and the backward traveling valve, characterized in that a part of a hydraulic circuit establishing connection between the hydraulic pressure source and the hydraulic clutches is formed on a front lid member that is detachably attached to close a front surface opening of the transmission case, and wherein the forward traveling valve, the backward traveling valve, and the master valve are attached on a front surface side of the front lid member.