A system and method of evaluating a radiation dose delivered to a patient receiving radiation therapy. The image signal compensation apparatus includes a lookup table and an image signal compensation unit. In switching from a two-wheel drive mode to a four-wheel drive mode, synchronization of the second disengaging mechanism first starts to increase the rotation speed of the driving-force transmitting unit, and next connects the first disengaging mechanism when a rotation speed of the driving-force transmitting unit side of the first disengaging mechanism matches that of an opposing side. The pintle further is coupled with a reinforced element which has at least one reinforced portion to wedge in the gap and press the inner wall of the pintle hole to provide a bracing torque thereby to enhance the steadiness of the structure. Each of the inner connecting conductors is electrically connected to the corresponding terminal and outer connecting conductors. When the detection sensor detects the case having been held by the user, the power supply unit supplies power to the imaging system, but not to the displaying unit, which is referred to as a tentative startup state.