A Rankine cycle (6) of a waste heat utilization device includes a circulation path (7) for circulating a working fluid therethrough, an evaporator (12) for causing heat to transfer from cooling water delivered from an internal combustion engine (2) to the working fluid to evaporate the working fluid, a superheater (10) for causing heat to transfer from the cooling water delivered from an exhaust gas heat exchanger (8) to the working fluid delivered from the evaporator to superheat the working fluid, an expander (22) for expanding the working fluid delivered from the superheater to produce driving force, a condenser (24) for condensing the working fluid delivered from the expander, and a pump (28) for feeding the working fluid delivered from the condenser to the evaporator. The evaporator, the superheater, the expander, the condenser and the pump are successively inserted in the working fluid circulation path.