To provide a suppressant for the oxidation and nitridation reaction of metals or a composite of the metals and organic matter or the organic matter which is capable of effectively suppressing reaction before the occurrence of a fire and is safe, inexpensive and highly versatile.

The back of a cap 19 is provided with desiccants 29 and therefore the consolidation of the suppressant (KCl, NaCl or mixture) for the reaction having the consolidation by the nature of the critical humidity of salt can be prevented. Even in case the humidity in a metallic bucket 3 rises, the humidity increased by the change in the color of a humidity indicator 11 is identifiable from outside. The state of the suppressant S1 in the metallic bucket 3 is visible from a hole 25, making it possible to surely prevent the overlooking of the state that the suppressant S1 is useless by absorption of moisture when needed. The consumption of the suppressant is arbitrarily regulatable to meet the reaction.