The 440C stainless steel is used for ball bearings and bevel gears in the control rod drive mechanism for the integral reactor, SMART. The friction characteristics of 400C stainless steel a investigated in sliding motion using the reciprocating tribometer which can simulate the operating conditions of the control rod drive mechanism. Highly purified water is used as lubricant, and the water is heated and pressurized in the autoclave. Friction force on the reciprocating specimens is measured by the load cells and transformed into friction coefficient. It is verified that frictional characteristic of the 440c steel is not drastically changed up to operating temperature and variation of friction coeffcient at operating temperature from room temperature to 160$^{circ}C$ is within 5%.