A torque-measuring device for measuring the engine output shaft on head-feeding combine harvesters was developed to investigate engine working load, an essential element in studies of fuel consumption and exhaust gas emissions. On most head-feeding combine harvesters, a pulley is fastened to an engine flywheel without a shaft. The power loss caused by the belt means engine torque should be measured between the flywheel and pulley. However, there is insufficient space to install conventional torque-measuring equipment. The torque-measuring device we developed was designed to be mounted between the flywheel and pulley. To make the device more compact, it was designed as a double-cylinder structure, with the deformation of the two torque-transmitting beams translated into a torque value. This device does not require irreversible alterations to be made to combines, and is designed to measure torque without any power loss. In static torque measurements, the margin of error of this device proved less than 6%, while the data measured during harvesting operations correlated with that of prior studies. Our results indicate that this device has good potential for use in further studies.