A work vehicle comprising: a vehicle body frame; a traveling device that is supported by the vehicle body frame; an engine acting as a drive source for the traveling device, the engine being provided at a front half portion of the vehicle body frame; a speed changing device that is configured to speed-change a driving force of the engine for transmitting the speed-changed force to the traveling device; a belt transmission mechanism that is configured to transmit the driving force of the engine to the speed changing device; a belt tension clutch that is configured to switch over the belt transmission mechanism between a transmitting state for transmitting the driving force to the speed changing device and a non-transmitting state that blocks transmission of the driving force to the speed changing device; a brake operating tool for performing a braking operation of the traveling device; and a coupling mechanism that is configured to activate the belt tension clutch for switching over the belt transmission mechanism into the non-transmitting state, in operative association with a braking operation on the brake operating tool, wherein a single transmission belt extends from an output shaft of the engine to an input shaft of the speed changing device; and the belt tension clutch includes a tension pulley that is configured to apply a tension to the transmission belt by coming in contact with the transmission belt, the belt transmission mechanism being switched to the non-transmitting state when tension application to the transmission belt by the tension pulley is released in response to the braking operation of the traveling device by the brake operating tool; characterized in that the speed changing device is a hydrostatic stepless speed changing device that is provided between a pair of left and right rear wheels that are configured to act as the traveling device. a vehicle body frame; a traveling device that is supported by the vehicle body frame; an engine acting as a drive source for the traveling device, the engine being provided at a front half portion of the vehicle body frame; a speed changing device that is configured to speed-change a driving force of the engine for transmitting the speed-changed force to the traveling device; a belt transmission mechanism that is configured to transmit the driving force of the engine to the speed changing device; a belt tension clutch that is configured to switch over the belt transmission mechanism between a transmitting state for transmitting the driving force to the speed changing device and a non-transmitting state that blocks transmission of the driving force to the speed changing device; a brake operating tool for performing a braking operation of the traveling device; and a coupling mechanism that is configured to activate the belt tension clutch for switching over the belt transmission mechanism into the non-transmitting state, in operative association with a braking operation on the brake operating tool, wherein a single transmission belt extends from an output shaft of the engine to an input shaft of the speed changing device; and the belt tension clutch includes a tension pulley that is configured to apply a tension to the transmission belt by coming in contact with the transmission belt, the belt transmission mechanism being switched to the non-transmitting state when tension application to the transmission belt by the tension pulley is released in response to the braking operation of the traveling device by the brake operating tool; characterized in that the speed changing device is a hydrostatic stepless speed changing device that is provided between a pair of left and right rear wheels that are configured to act as the traveling device.