PURPOSE: To convert solar energy efficiently by arranging the parallel concave mirror so that its upper and lower, and right and left face the solar rays at right angles, and converging the rays in s beltlike shape.

CONSTITUTION: The arc connecting the upper end 8 and lower end 9 of the parallel concave mirror 1 forms part of the circumference having its center at a center point 10, and a metallic pipe 2 is arranged where reflected light is converged. Further, the concave mirror 1 is provided rotatably around a shaft 5 through a wheel 6 so as to track the sun, and the upper and lower, and right and left parts or the concave mirror 1 face the sun at right angles. Then, the light is converted o the metallic pipe 2 not through a single spherical mirror, but through the parallel concave mirror 1 in a convergent zone. Consequently, the solar energy is converged in the beltlike shape to perform efficient energy conversion, e.g. raise the water temperature in the metallic pipe.