A silicon nitride sintered body comprising β-sialon expressed by a composition formula of Si6−ZAlZOZN8−Z, wherein z value being the dissolved amount is 0.1 to 1, as a main phase, a grain boundary phase and Fe silicide particles. The grain boundary phase contains RE (Group III elements in the periodic table)-Al—Si—O, and component ratios of Al, Si and RE in terms of Al2O3, SiO2, RE2O3, respectively is 5 to 50 mass % of Al2O3, 5 to 20 mass % of SiO2, and the balanced amount of RE2O3, the grain boundary phase is contained in a range of 20 volume % or less to 100 volume % of the sintered body, and the Fe silicide particles is contained in 0.02 to 3 mass % in terms of Fe to 100 mass % of the sintered body. Its high thermal shock resistance provides suitable applications to members for molten metal, hot working, and digging.