A viscous fluid type heat generating apparatus having a housing forming a cylindrical heat-generating chamber having a cylindrical wall surface and an axially spaced flat annular wall surface, and a rotatably supported rotor element having a cylindrical base portion and an axially extending tubular portion integral with the base portion forming a substantially cylindrical outer face and a cavity portion used as a fluid-storing chamber, the cylindrical portion of the rotor element cooperating with the cylindrical wall surface of the housing to define a main part of a heat-generating gap holding a viscous fluid which generates heat in response to an application of a shearing force to the viscous fluid in response to the rotation of the rotor element. The heat generating apparatus further having an intercommunicating passage providing a fluid communication between the heat-generating gap and the fluid storing chamber to thereby cause a circulation of the viscous fluid during the rotation of the rotor element, and a flow rate controlling actuator controlling an amount of circulation of the viscous fluid in response to a change in the rotating speed of the rotor element.