To provide such a fireproofing method as to raise the reliability on fireproofing treatment for blocking the opening of a long body piercing part by a thermally expansive material, while raising the efficiency of the thermally expansive fire-resistant material, in the fireproofing treatment of the long body piercing part in a fireproofing section, and further to enable the execution work of the fireproofing treatment to be performed efficiently.

In the thermally expansive fire-resistant material M with a resin material M1 and an expansive material are kneaded as its main components, a bar- or fiber-shaped contractile material M2, which contracts by heating, is so contained as to be oriented in a predetermined direction. A fire-resistant molded item 1 is made of the thermally expansive fire-resistant material, and the contractile material is oriented along the surface of the fire-resistant molded item. When inserting the fire-resistant molded item 1 into the space of the long body piercing part so as to perform fireproofing treatment, it is arranged so that the contractile material may be oriented in the longitudinal direction of the long body. The orientation of the contractile expansive material M2 can be performed by extending the thermally expansive fire-resistant material M or the fire-resistant molded item 1.