A viscous fluid type heat generator including a housing assembly in which a fluid-tight heat generating chamber confining therein a viscous fluid to which a shearing action is applied by a disc-like rotor element rotated by a drive shaft, and having inner wall surfaces confronting outer surfaces of the rotor element, the inner wall surfaces of the fluid-tight heat generating chamber and the outer faces of the rotor element defining a gap in which the viscous fluid is held, the rotor element being provided with one or more through-holes formed in an outer peripheral portion and a radially inner portion thereof with respect to the axis of rotation of the rotor element so that the through-holes cooperate with one or more non-circumferentially extending elongate indentations provided in the inner wall surfaces of the fluid-tight heat generating chamber during the rotation of the rotor element to expand a heat generating region formed by the gap. The expansion of the heat generating region formed by the gap increases a restraint acting against movement of the viscous fluid caused by the rotation of the rotor element so as to increase friction and a shearing force acting on the viscous fluid, and heat generation by the viscous fluid is increased.