Disclosed is a light-collecting heliostat using flat mirrors of enhanced light-collecting efficiency. The gradients of low-price flat mirrors are adjusted when reflecting sunlight by the heliostat equipped with the flat mirrors, thereby causing reflection focal areas having the same size as each of the mirrors to overlap, in the same number as the number of the reflective plates constituting the heliostat, on a heat collecting unit of collecting lights, so that a high temperature light-collecting focal area with a uniform temperature distribution is obtained.