An overhead traveling crane system, wherein at least two locking members (25a) are mounted vertically slidably on a lifting device (15), a stopper (25b) and a contact member are fixed to the upper and lower end parts of each locking member (25a), respectively. A non-contact sensing device is fixed to the underside of the lifting device (15), and a sensor element (27) is fixed to the locking members (25a). The lowering of the locking members (25a) is stopped when the contact means is brought into contact with a reference position, and the lowering of the lifting device (15) is stopped when the lifting device (15) is lowered further so as to move the sensing device on the lifting device (15) side closely to the sensor element on the locking members (25a). Even though a general-purpose overhead traveling crane is used, the vertical positioning accuracy of the lifting device installed on the overhead traveling crane is increased.