To rapidly release fluid inside a high-pressure apparatus to the outside when the fluid inside the high-pressure apparatus reaches an abnormally high temperature in a fusible plug fitted to the high-pressure apparatus holding the high-pressure fluid therein and releasing the fluid in the apparatus by allowing a low melting point alloy incorporated therein to melt at the time of abnormally high temperature.

A communication hole 13 having a cross section in such a shape that a plurality of grooves 14 are collected is drilled in the soluble plug. When the inside of the high-pressure apparatus reaches the abnormally high temperature, the plug starts to melt starting at the grooves 14 of the communication hole 13 to rapidly open that portion to the outside air side end.