A position detection device for a horizontal articulated robot includes a camera for imaging the robot or a work as an imaging object, a control section for calculating a location of the imaging object from an image, an acquisition section (I/O) for obtaining the drive amounts of first and second electric motors of the robot, and a storage section for storing the calculated location of the imaging object and the drive amounts so as to correspond to each other. A common trigger signal for detecting the location of the imaging object is input to the camera and the I/O. The camera starts to image the imaging object in response to the input of the trigger signal. The I/O starts to obtain the drive amounts in response to the input of the trigger signal.