A riding work vehicle, comprising: right and left wheels as main driving wheels that are respectively driven independently for traveling; at least one caster wheel as a steering control wheel whose operational state is selectable between free traveling and forced traveling and also between free steering and forced steering; a working machine that is operable for work on the ground; a traveling motor configured to drive the caster wheel for traveling; a steering motor configured to steer the caster wheel; a traveling system clutch that is provided in a traveling system power transmission path for transmitting the power from the traveling motor to an axle of the caster wheel and is configured to disable transmission of the rotational force from the axle to the traveling motor in a state where the traveling motor is deactivated; and a steering system clutch that is provided in a steering system power transmission path for transmitting the power between the steering motor and a steering shaft for the caster wheel and is configured to disable transmission of the rotational force from the steering shaft to the steering motor in a state where the steering motor is deactivated wherein the traveling system clutch is configured to switch its operational state between an engaged state and a disengaged state according to a control signal input from the control unit, the steering system clutch is configured to switch its operational state between an engaged state and a disengaged state according to a control signal input from a control unit, characterised in that the control unit is configured to constantly engage the steering system clutch when the traveling system clutch is engaged. right and left wheels as main driving wheels that are respectively driven independently for traveling; at least one caster wheel as a steering control wheel whose operational state is selectable between free traveling and forced traveling and also between free steering and forced steering; a working machine that is operable for work on the ground; a traveling motor configured to drive the caster wheel for traveling; a steering motor configured to steer the caster wheel; a traveling system clutch that is provided in a traveling system power transmission path for transmitting the power from the traveling motor to an axle of the caster wheel and is configured to disable transmission of the rotational force from the axle to the traveling motor in a state where the traveling motor is deactivated; and a steering system clutch that is provided in a steering system power transmission path for transmitting the power between the steering motor and a steering shaft for the caster wheel and is configured to disable transmission of the rotational force from the steering shaft to the steering motor in a state where the steering motor is deactivated wherein the traveling system clutch is configured to switch its operational state between an engaged state and a disengaged state according to a control signal input from the control unit, the steering system clutch is configured to switch its operational state between an engaged state and a disengaged state according to a control signal input from a control unit, characterised in that the control unit is configured to constantly engage the steering system clutch when the traveling system clutch is engaged.