To provide a sintered silicon nitride with conductivity and densification, an oxide of titanium group elements, such as titanium oxide, hafnium oxide, zirconium oxide and the like, aluminum oxide and/or aluminum nitride is added as needed to silicon nitride-oxidant of rare-earth elements-aluminum oxide system or silicon nitride-oxide of rare-earth elements-magnesia system, and then specified quantity of carbon nonotube (CNT) is added to the above mixture. CNT generates silicon carbide after the reaction with contiguous or proximal silicon nitride and the like depending on the sintering duration at high temperature. Since silicon carbide is generated along with nanotubes, the silicon carbide functions as conductor with excellent heat resistance, corrosion resistance and the like.