To provide a fire spread preventing device for facilitating the inspection of the inside of a case member.

The fire spread preventing device includes: a drain collecting pipe 2 disposed passing through a slab 7 of a ceiling 6, and having at least an outer layer being fire-resistant; a non-fire-resistant pipe 4 connected to a joint part 14 at the lower part of the drain collecting pipe 2; a cylindrical nonflammable case member 19 covering the outer periphery of the non-fire-resistant pipe 4 including the vicinity of the lower end of the drain collecting pipe 2; a thermally expansive member 20 disposed downward of the lower end of the drain collecting pipe 2 between the inner peripheral face of the case member 19 and the outer peripheral face of the non-fire-resistant pipe 4; and a suspension member 21 having an upper part fixed to the slab or a refractory product supported by the slab for supporting the case member 19. The case member 19 has a plurality of case split bodies 29, 30 splittable in the circumferential direction, joining means 31 for joining the plurality of the case split bodies 29, 30 together into a cylindrical shape, and a connecting means 32 for removably connecting the suspension member 21 to the case member 19.