PURPOSE: To improve the accuracy of detecting the puncture by holding a limit rod at a curved state conforming to the surface shape of the tire, and making a limit machine rack to be freely moved back and forth.

CONSTITUTION: The limit rod 7 is formed in a U shape so as to surround a part of the outer periphery of the tire 6 and to connect pieces of metal 20 one another. The curved state of the limit rod 7 is maintained to be approximately conformal with the surface shape of the tire. The interval between the limit rod 7 and the tire 6 is adjusted by an adjusting screw 25, and rotation resistance is adjusted by an adjusting screw 8. A limit switch part 9, the limit rod 7, and a photoelectric tube 11 are placed on the limit machine rack 24 so that they are freely moved back and forth within the range of d by the driving of a motor 10. The limit machine rack 24 is supported so that it can be set in correspondence with the size of the tire by a sliding shaft 23 and can be moved back and forth within the range of the distance e. When the limit switch detects the change in the outer diameter of the tire surface due to the puncture, the limit switch is turned ON, the tire 6 is unloaded, and the warning is sounded.