Waste heat utilization device for an engine

Comprising a Rankine cycle system having an expander bypass passage and a bypass valve for opening and closing the expander bypass passage, in the waste heat utilization device for an engine for transmitting the engine down the output of the Rankine cycle system, regardless of the open or closed state of the bypass valve, Rankin estimated accurately output cycle apparatus enabling appropriate output control of the engine. Output calculation section 42 includes a torque estimator 421 for estimating the torque of the expander 23. The torque estimation portion 421 has a second torque estimation equation first torque estimation equation and the bypass valve 27 the bypass valve 27 corresponding to the state of being open is corresponding to the state of being closed. The output calculation section 42 calculates the output of the Rankine cycle device 2A on the basis of the torque estimated value by the first torque estimation value or the second torque estimation equation by the torque estimation formula. The output of the calculated rankinite cycle device 2A is output to the engine control unit 12.