To enable a sun position detecting sensor incorporated in a sunlight collecting device to precisely detect the sun's position regardless of rather cloudy or hazy weather conditions and foreign objects such as dust clinging thereto, so that the sunlight collecting device can track the sun's motion accurately.

This sun position detecting sensor comprises a sunlight incident hole 2 provided in the top panel of a casing 1; a position detecting element 3 provided on the inner surface of the bottom panel of the casing 1 so that sunlight incident on the inside of the casing 1 through the incident hole 2 is split and taken from electrodes placed on both sides of the surface layer of the element to detect the incident position of the sunlight according to its output; and a signal processing circuit 4 for discriminating the center of gravity of the incident sunlight detected by the position detecting element 3.