A method for manufacturing a resin-based composite material includes: a stage in which prepregs are stacked on a jig; a stage in which the stacked prepregs and the jig are covered and pressurized heat treatment is applied thereto to form a first semi-molded article and a second semi-molded article; a stage in which board thicknesses of the first semi-molded article and the second semi-molded article are measured, a stage in which the number of additional plies is determined based on the measured board thicknesses, a desired board thickness of the resin-based composite material, and physical properties of the additional plies; and a stage in which a layered product is formed by stacking the predetermined number of additional plies between the first semi-molded article and the second semi-molded article, the layered product and the jig are covered with a bagging material, and pressurized heat treatment is applied thereto.