PURPOSE: To obtain a fall preventive method in which an amplifier cover can be removed without entangling a chain or the like used to prevent a fall by forming a groove on the amplifier cover and using a support ring or the like which can be moved freely in the groove.

CONSTITUTION: A groove 9 is formed on the outer circumference of an amplifier cover 8. A support ring 10 which supports the amplifier ring 8 is formed out of two half rings whose inside diameter is larger than the inside diameter of the groove 9 and smaller than the outer circumference of the amplifier cover 8, and one end is coupled with a link. After the ring 10 was mounted on the groove 9, a chain 11 is attached to the lower end of the support rod of the support ring 10, and its end is fixed to an amplifier case body. The support ring 10 which is installed inside the groove 9 can be moved freely inside the groove 9. When the amplifier cover 8 is removed, the support ring is always situated at the lower part of the amplifier cover 8 due to the own weight of the chain 11, and the chain 11 is not entangled. This can be applied not only to the fall prevention of the amplifier cover 8 at a transmitter but also to a case in which a lid is turned and removed.