Driving wheels and non-driving wheels are installed to a lower portion of a case body. The driving wheels are driven by drive devices, respectively. A control device controls a drive operation of the drive devices. An angle sensing device senses a tilt angle of the case body about a rotational axis of the driving wheels. In a case where the tilt angle of the case body, which is sensed with the angle sensing device, is equal to or larger than a predetermined tilt angle in a state where the driving wheels contact a ground while the non-driving wheels are lifted away from the ground, the control device controls the drive devices in such a manner that the case body is held in a self-standing state with the driving wheels while keeping the non-driving wheel away from the ground.