To provide a fire-protection structure for an outlet box that can prevent fire, smoke, etc. from passing through the outlet box when the outlet box is exposed to heat such as fire or the like, and a construction method for the fire-protection structure.

An opening portion side of an outlet box 1 is installed on a wall 40 having a through-hole 43 so as to cover the through-hole, a thermal-expansion type fire-resisting seal material 80 is installed between the wall and the outlet box, an electrical wire cable group 50 is inserted through an insertion hole of the outlet box, and a thermal-expansion type fire-resisting seat 20 of a low thermal expansion start temperature and a thermal-expansion type fire-resisting seat 30 of a high thermal expansion start temperature are combined and installed at the back plate side in the outlet box.