The invention relates to a position detection device, an image reading device, an image forming device and a position detection method, and is used for reducing the error of a position detection result caused by stretching due to heating of the reading equipment. The position detection device comprises a control reading device (201) and a first position detection unit for detecting the shape of the processed object and the position of the image pattern on the processed object as a first detection result. (111), and controlling the reading device to correspond to the reading device on the position reference member. (201) is used as a second detection result to be detected as a second detection result. (112) and detecting the reading device according to the first detection result and the second detection result. (201) and corrects the processing position of the processing object.