To provide a seizure-proof agent having seizure-proof effect even under circumstances at high-temperatures of as high as 800°C, and to provide an internal engine fitting component having an outer circumference threaded portion coated therewith.

The seizure-proof agent includes: a solid lubricant comprising antimony oxide, graphite, bismuth and calcium oxide; and a pasty non-solid lubricant. For the respective amounts of the above components in the agent meets the following relationships: 17 mass%≤A≤29 mass%; 1 mass%≤B≤10 mass%; 9 mass%≤C≤15 mass%; and 7 mass%≤D≤30 mass% (wherein, A is the antimony oxide content of the whole agent; B is the graphite content of the whole agent; C is the bismuth content of the whole agent; and D is the calcium oxide content of the whole agent).