The present invention relates to a method for manufacturing a concrete block, comprising the steps of: measuring the planned alignment considering the horizontal alignment, slope and cant of a site on which railway tracks are to be laid; arranging a plurality of first temporary assembly supports corresponding to the measured horizontal alignment; installing first temporary rails on the first temporary assembly supports, and adjusting the slope and cant in between the first temporary rails to correspond to the measured slope and cant; installing a plurality of first molds on the first temporary rails, following along therewith, so that the slope and cant correspond to the measured slope and cant; installing a pair of second molds along the longitudinal direction of the first temporary rails, thereby closing off the upper lateral sides of the first molds; arranging, to the horizontal alignment, a plurality of second temporary assembly supports corresponding to the first temporary assembly supports, on the outer sides of the first temporary assembly supports; installing second temporary rails on the second temporary assembly supports so that a vertical alignment correspond to the vertical alignment of the on-site roadbed; pouring concrete; forming the concrete surface with a finisher moving along the second temporary rails; curing the concrete; and separating the cured concrete from the first and second molds, and subsequently turning the concrete over.