the invention aims to offer a method to manufacture a high - strength , high - reliability and low cost silicon nitride based sintered body which is not affected by the amount of metal impurities contained in the silicon nitride powder , without using high - purity silicon nitride powder , and can be sintered for a short sintering time . the invention uses silicon nitride and sintering aids , and the powder mixture containing 500 - 5000 ppm metal impurities is sintered at temperatures ranging from 1300 °- 1900 ° c ., and under the conditions wherein the product of sintering temperature and sintering time ranges from 1 × 10 5 to 10 × 10 5 ° c . · seconds .