To perform strong kneading by a simple process and inexpensive equipment and to satisfactorily ensure a heating and mixing time at a high temp. by arranging a heating device heating a cylindrical body and heating the kneaded matter flowing through the cylindrical body in succession to the heating in a kneader.

A cylindrical metal body 12 is connected to the discharge port 7 of a continuous kneader and an electric heater 13 is attached to the cylindrical body along with the continuous kneader 1 to heat the cylindrical body. 100 pts. of straight chain dimethylpolysiloxane blocked at both terminals thereof by a vinyldimethylsilyl group and having viscosity of 10,000cSt at 25°C and 67 pts. of a wet silica fine powder with a specific surface area of 180m2/g and bulk density of 0.1kg/l being a filler are continuously supplied to a supply port 2 as main agents by using a gear pump and a powder quantitative feeder 3. The kneaded matter in the cylindrial body 12 is heated at 80-300°C for 1min or more. Therefore, strong kneading is performed by a simple process and a heating and mixing time at a high temp. can be satisfactorily ensured.