A torque detection device for a power steering which is less liable to be influenced by external factors or by a bending force exerted on a shaft. In the torque detection device, a torque is generated between an input shaft, which is turned interlockedly with a steering handle for operating the traveling direction of a vehicle, and an output shaft turned interlockedly with the input shaft so as to steer the vehicle. An assisting force is exerted on the output shaft by an assisting unit that is determined based on the detection result. The torque detection device is provided between the input shaft and the output shaft and includes a cam mechanism by which a torque generated between the input shaft and the output shaft is converted into a thrust force, and a pressure sensor for detecting the thrust force into which the torque is converted by the cam mechanism.