A work vehicle comprising: an engine; a transmission mechanism for transmitting a rotational drive power of the engine to a traveling device; a speed changer device provided in the transmission mechanism and capable of changing the vehicle speed by speed-changing the rotational drive power; a parking brake mechanism capable of restricting the operation of the transmission mechanism; a single operation lever (19A;300) that is manually pivotable and capable of speed changing operations of the speed changer device and a braking operation of the parking brake mechanism; a first link mechanism (44;100) for linking the operation lever with the speed changer device; a second link mechanism capable of linking and release of linking between the operation lever and the parking brake mechanism; a locking mechanism (18;500) including a retaining portion connected to a component included in the operation lever and a retained portion fixed to a component which remains stationary relative to the operation lever, and capable of maintaining the parking brake mechanism under a condition of restricting the operation of the operation lever through restriction of the position of the operation lever; wherein the operation lever includes, as speed changing operation paths thereof, a neutral path corresponding to a neutral state of the speed changer device and a speed changing path extending straight from the neutral path and corresponding to a speed changing state of the speed changer device; the braking operation is effected only by a pivotal operation of the operation lever; the operation lever includes, as brake operating paths thereof, a linking path extending from the neutral path along a direction intersecting the speed changing path, a braking path extending from the terminal end of the linking path along a direction intersecting the linking path, and a locking path (84,85) extending at least form the terminal end of the braking path along a direction intersecting the braking path; when the operation lever is operated either to the speed changing path or the neutral path, the second link mechanism does not link the operation lever with the parking brake mechanism; when the operation lever is operated from the neutral path to the linking path, the second link mechanism links the operation lever with the parking brake mechanism; when the operation lever is operated to the braking path, the parking brake mechanism is actuated; when the operation lever is operated to the locking path (84,85), the locking mechanism is actuated; and when the operation lever is operated to the locking path (84,85), the retaining portion is retained to the retained portion. an engine; a transmission mechanism for transmitting a rotational drive power of the engine to a traveling device; a speed changer device provided in the transmission mechanism and capable of changing the vehicle speed by speed-changing the rotational drive power; a parking brake mechanism capable of restricting the operation of the transmission mechanism; a single operation lever (19A;300) that is manually pivotable and capable of speed changing operations of the speed changer device and a braking operation of the parking brake mechanism; a first link mechanism (44;100) for linking the operation lever with the speed changer device; a second link mechanism capable of linking and release of linking between the operation lever and the parking brake mechanism; a locking mechanism (18;500) including a retaining portion connected to a component included in the operation lever and a retained portion fixed to a component which remains stationary relative to the operation lever, and capable of maintaining the parking brake mechanism under a condition of restricting the operation of the operation lever through restriction of the position of the operation lever; wherein the operation lever includes, as speed changing operation paths thereof, a neutral path corresponding to a neutral state of the speed changer device and a speed changing path extending straight from the neutral path and corresponding to a speed changing state of the speed changer device; the braking operation is effected only by a pivotal operation of the operation lever; the operation lever includes, as brake operating paths thereof, a linking path extending from the neutral path along a direction intersecting the speed changing path, a braking path extending from the terminal end of the linking path along a direction intersecting the linking path, and a locking path (84,85) extending at least form the terminal end of the braking path along a direction intersecting the braking path; when the operation lever is operated either to the speed changing path or the neutral path, the second link mechanism does not link the operation lever with the parking brake mechanism; when the operation lever is operated from the neutral path to the linking path, the second link mechanism links the operation lever with the parking brake mechanism; when the operation lever is operated to the braking path, the parking brake mechanism is actuated; when the operation lever is operated to the locking path (84,85), the locking mechanism is actuated; and when the operation lever is operated to the locking path (84,85), the retaining portion is retained to the retained portion.