Combustor, boiler and assembling method of combustor

The invention discloses a combustor, a boiler and an assembling method of the combustor. The combustor is provided with: a fuel nozzle (18) that ejects fuel gas, in which fuel and air are mixed, intoa hearth; a combustion air nozzle that blows air into the hearth from the periphery of the fuel nozzle; a flame stabilizer (3) that is disposed within the fuel nozzle and that widens toward the hearth-side end surface of the fuel nozzle; and a rectifying section (4) that is disposed on an extension line on the upstream side in the fuel gas flow direction with respect to the flame stabilizer. Thisflame stabilizer is provided with: a base material; an inclined section (8) that is provided to the base material, has an inclined surface formed so as to protrude from the upstream side of the hearth-side end surface of the base material toward the hearth-side end surface of the fuel nozzle, and is formed so as to protrude from the hearth-side end surface of the base material; a cover part (9) which is connected with the