To extend the life of a viscous fluid by avoiding most of the viscous fluid in a heating chamber from being continually subjected to shearing action when in the gap between a rotor and the wall surface of the heating chamber.

A heating chamber 7 is formed between a front housing 1 and a rear housing 2. A support shaft 11 is eccentrically projected from the large- diameter part 8a of a drive shaft 8 supported against the front housing 1, and a columnar rotor 12 is secured to the support shaft 11 in such a way as to be incapable of relative rotation when its center coincides with the center of the support shaft 11. The rotor 12 is secured to the support shaft 11 in such a manner that the gap between its first end face 12a and the front end face of the rear housing 2 is of a predetermined size such that shearing action can be efficiently imparted to a viscous fluid existing in the gap θ. A storage chamber 13 and an annular water jacket 14 are defined between the rear face of the rear housing 2 and the front end face of a rear plate 3 to correspond to the heating chamber 7.