Recently, torque has become very important to various control systems and diagnoses of automobile engines. We have developed a miniature torque sensor based on the magnetostrictive effect, which is capable of accurately detecting the torque produced by an automobile engine. The sensor was installed in the last main bearing of the engine ( TOYOTA 4A-FE ; 1.6-liter 4-cylinder ) crankshaft so as to directly pick up the torque generated in the crankshaft. This sensor was composed of two head-type detecting elements, which were placed opposite to each other through the crankshaft in order to eliminate the influence of the off-center motion of the shaft on the sensor output. In addition, a commercial crankshaft made of nodular cast iron ( JIS code : FCD70 ) was adopted, taking account of high sensor sensitivity and mechanical stiffness. Tests using an engine dynamometer showed that this sensor could clearly detect peculiar instantaneous torque wave with four peaks during two crankshaft rotations, corresponding to four cylinder combustions. As a result of in-vehicle experiments, furthermore, this sensor was found to detect the true torque produced by an engine and to be available for on-board use. In the future, this sensor will be extremely promising for use in various engine control systems.