To provide a protection block against fire used for cable penetration part in a fire wall to enable execution of construction for replacement and extension of a cable, in a short time.

A protection block against fire has a penetration hole in its center and is composed of two half blocks 20H, divided by the surface which divides the penetration hole into two equal parts. Each block 20H is composed of a hard block 28, cushioning blocks 30, refractory materials 32 against fire and a sheet 34. The hard block 28 has a function for maintaining its shape. The materials 32 have characteristic of thermal expansion. The sheet 34 wraps the hard block 28, the cushiony blocks 30 and the materials 32 and has characteristic of flame resistance. The inside diameter of a penetration hole part 30a in the cushioning blocks 30 is smaller than the inside diameters of penetration hole parts 28a, 32a in the hard block 28 and the refractors materials 32. The required number of the protection blocks against fire are disposed in a cable penetration opening of the fire wall and hold cables and a sealant, to close the opening.