A dolly configured to be towed by a tractor , the dolly comprising: a wheel ; a brake device configured to apply a braking force to the wheel ; and a towbar including a coupling hole into which a drawbar of the tractor is insertable, wherein when the drawbar is inserted into the coupling hole , the dolly is coupled to the tractor via the towbar and the drawbar , and the brake device is configured to switch from a braking state in which a braking force is applied to the wheel to a non-braking state in which the wheel is released from the braking force when inserting the drawbar into the coupling hole , and to switch from the non-braking state to the braking state when removing the drawbar from the coupling hole , characterized in that the brake device includes a braking portion that configured to apply a braking force to the wheel , a lever that is configured to interlock with the braking portion , and an urging portion that is configured to urge the lever and the braking portion , the brake device is configured so that when the drawbar is removed from the coupling hole , the lever is urged by the urging portion to at least partially close the coupling hole and the braking portion is urged by the urging portion to switch to the braking state, and the brake device is configured so that when the drawbar moves the lever , which closes the coupling hole , against an urging force of the urging portion and is inserted into the coupling hole, the braking portion interlocks with the lever against the urging force of the urging portion to switch to the non-braking state. a wheel ; a brake device configured to apply a braking force to the wheel ; and a towbar including a coupling hole into which a drawbar of the tractor is insertable, wherein when the drawbar is inserted into the coupling hole , the dolly is coupled to the tractor via the towbar and the drawbar , and the brake device is configured to switch from a braking state in which a braking force is applied to the wheel to a non-braking state in which the wheel is released from the braking force when inserting the drawbar into the coupling hole , and to switch from the non-braking state to the braking state when removing the drawbar from the coupling hole , characterized in that the brake device includes a braking portion that configured to apply a braking force to the wheel , a lever that is configured to interlock with the braking portion , and an urging portion that is configured to urge the lever and the braking portion , a braking portion that configured to apply a braking force to the wheel , a lever that is configured to interlock with the braking portion , and an urging portion that is configured to urge the lever and the braking portion , the brake device is configured so that when the drawbar is removed from the coupling hole , the lever is urged by the urging portion to at least partially close the coupling hole and the braking portion is urged by the urging portion to switch to the braking state, and the brake device is configured so that when the drawbar moves the lever , which closes the coupling hole , against an urging force of the urging portion and is inserted into the coupling hole, the braking portion interlocks with the lever against the urging force of the urging portion to switch to the non-braking state. <EOS>