the stored captured image step s 33 the same method as the method that is used at step s 21 for example may be used for the detection processing the coordinates of the centers of the first circle 101 and the second circle 102 that are identified by the detection processing are indicated as l1 m1 n1 and l2 m2 n2 respectively in a case where the detection processing has been performed at step s 33 the marker position and the marker angle of the marker 120 are computed a marker position of the detected marker 120 is specified as l1 m1 n1 based on the coordinates of the center of the identified first circle 101 based on the coordinates l1 m1 n1 of the center of the identified first circle 101 and the coordinates l2 m2 n2 of the center of the second circle 102 a marker angle u03b8 3 of the detected marker 120 is obtained as u03b8 3 tan u2212 1 m2 u2212 m1 l2 u2212 l1 if the marker position and the marker angle of the marker 120 have not been specified for failure of the detection processing at step s 33 no at step s 35 the screen for indicating that the marker 120 has not.