To surely preclude a connection wire rope from being separated, and to prevent a testing vehicle from damaging a dolly device.

A connecting-wire releasing lever 21 constituting the respective front and rear dolly devices Da, Db is collided with a striker S to release an engaged state between an engaging part 21a thereof and hook bodies 2 and a coming-off preventive body 18 of a hook device F, and the front and rear hook bodies 2 hooked with the respective connecting wire ropes Wa, Wb, and the coming-off preventive body 18 for closing opening faces of hooking parts 2a of the front and rear hook hook bodies 2 are turned along a direction contrary each other around an axis of the same turning shaft 17 as the center to be retracted to an under side of a dolly main body 8.