PURPOSE: To efficiently receive heat of light to heat water, etc., by collecting heat of light to a pipe colored in black or another by a groove-like convex mirror.

CONSTITUTION: Heat of light is received by a pipe 2 colored in black or another and the whole surface of a groove-like convex mirror 1, so the heat of light received by the groove-like convex mirror 1 is reflected and collected to the pipe 2 colored in black or another. Therefore, the pipe 2 colored in black or another also receives the heat of light collected by the groove-like convex mirror 2 in addition to the heat of light directly radiated on the pipe 2. Thereby, heat of light is efficiently received to heat water, etc., in the pipe 2 colored in black or another, so that high-temperature hot-water can be obtained even during cold season.