In a drive system, there is provided a waste heat recovering device forming a Rankine cycle by an evaporator for heating water with waste heat of an internal combustion engine to generate high-pressure vapor, the internal combustion engine being connected to a transmission, a displacement-type expander for converting high-pressure vapor generated by the evaporator to an output with constant torque, a condenser for liquefying low-pressure vapor discharged from the expander, and a feed pump for supplying water liquefied by the condenser to the evaporator. The expander is connected to a power generator/motor via a planetary gear mechanism, and the expander is connected to an output shaft of the internal combustion engine via the planetary gear mechanism and a belt-type continuously variable transmission. A change gear ratio of the belt-type continuously variable transmission is controlled such that a rotational speed of the internal combustion engine and a rotational speed of the expander are matched with each other and are transmitted to the transmission. Hence, it is possible to effectively drive the driven portion by using the output of the expander of the waste heat recovering device.