An acceleration sensor (10) is attached to a collimator (12) and detects an acceleration of the collimator (12), and a speed calculation unit that calculates the speed of the collimator 12 on a basis of the acceleration detected by the acceleration sensor (10). When the speed of the collimator (12) exceeds a setting speed that is set in advance, a lifting or lowering of an arm (13) is stopped by attaching a permanent electromagnet (42) to a stopper plate (43). In addition, a warning message as a warning indication is displayed on a display unit, and a warning sound as a warning indication is generated from a speaker. Accordingly, damage to an apparatus is prevented.