1. A position detector for detecting a position on a given plane comprising: a first controller that displays a target point on the given plane; a second controller that adds a known standard on the given plane in the vicinity of the target point with the location of the standard known; an image sensor having an image plane on which an image of the given plane is formed with an image of the standard included, a point in the image of the given plane which is formed at a predetermined position of the image plane corresponding to the point to be detected on the given plane; an image processor that identifies the image of the standard on the image plane; a processor that calculates the position of the point to be detected on the basis of the identified image of the standard on the image plane.