A first guide rail (11), and a second guide rail (12) and a third guide rail (13) that are parallel to each other are installed on a base (2) so as to be perpendicular to each other, and these guide rails are rotated about shafts (4) installed on both ends. When the guide rails are rotated, an indication bar (3) installed on a rotor (1) is moved synchronously with the movement of the guide rails, so that the rotor (1) is also rotated. A slider (22) installed on the indication bar (3) slides along a slit (21) of the third guide rail (13). Then a rotation angle of the rotor (1) about the indication bar (3) is determined by the distance between the guide rails.