The present invention relates to a reinforcement of foundation which comprises at least two base steel plates arranged to be upright with respect to the ground and shaped as a plate with a cutaway formed at a top portion thereof, a reinforced steel plate coupled to upper portions of both ends of the base steel plates, fastening steel rods placed to extend in a longitudinal direction of the base steel plate and coupled to the reinforced steel plate, and a connection steel rod bored sequentially through the base steel plates and coupled to the base steel plates. According to the present invention, huge concentrated load exerted on a foundation can be uniformly distributed, and thus, load transmitted from a pillar or column installed on the foundation can be stably supported. Further, the thickness of foundation can also be reduced as compared with the prior art, and thus, the excavation can be made shallow. Accordingly, the period and expense of construction can be reduced.