PURPOSE: To enable a correct chasing accuracy by detecting the position of the sun as a declination and hour angle.

CONSTITUTION: A two-dimensional position sensor 9 detects the light passing through a center axis 6 of a pinhole and outputs the current proportionate to the light receiving position which is on the sensor surface. Due to a detecting head 1 rotating clockwise, now then, the position of the sun is initially positioned to + side than the hour angle of a center axis 6, so the hour angle output current which is from the sensor 9 is started from + maximum output as well and when the hour angle of the center axis 6 and the hour angle of the sun position are allowed to coincide, the hour angle current goes to zero. Consequently the output value of an encoder 3 of the time of the hour angle output current of the sensor 9 being zero shows the hour angle of the sun position. The output current of the declination of the time of the hour angle output current of the sensor 9 being zero shows then the value proportionate to the declination. By the hour angle output current and declination output current, the hour angle of the sun position and declination are obtd. from a detecting circuit 20 of the sun position and a correct chasing is enabled.