A method for producing a resin-impregnated fiber bundle roll body, comprising: an unwinding step to take off a fiber bundle from a bobbin; a winding step to roll up the fiber bundle on a winding core rotating around a fixed axis through a movable winding head to prepare a product; and a leading step to lead the fiber bundle taken off in the unwinding step to the winding step between the unwinding step and the winding step, wherein the leading step or the winding step includes a resin adhesion operation to impregnate the fiber bundle with a resin, and the winding step includes a fiber content calculation operation to calculate a fiber content V f in % in a layer of the resin-impregnated fiber bundle being rolled up on the winding core of an intermediate product to control any one of (i) to (iv) according to the fiber content V f in %: (i) a resin adhesion amount in the resin adhesion operation; (ii) a winding tension of the fiber bundle applied to the intermediate product; (iii) a removal amount of a surplus resin layer generated on an outer surface of the intermediate product; and (iv) a resin viscosity in the intermediate product, wherein the winding step further includes a resin-impregnated fiber bundle layer thickness calculation operation to calculate a thickness t FRP of the layer of the resin-impregnated fiber bundle and then the fiber content calculation operation is performed by using the thickness t FRP, characterized in that the winding step further includes an outer diameter measurement operation to measure an outer diameter of the winding core or the intermediate product, and the thickness t FRP of the layer of the resin-impregnated fiber bundle, formed between a first time t 1 and a second time t 2 later than first time t 1, is calculated by using: a first outer diameter d 1 of the winding core or the intermediate product at the first time t 1; and a second outer diameter d 2 of the winding core or the intermediate product at the second time t 2, the first and second outer diameters d 1 and d 2 being measured by the outer diameter measurement operation. an unwinding step to take off a fiber bundle from a bobbin; a winding step to roll up the fiber bundle on a winding core rotating around a fixed axis through a movable winding head to prepare a product; and a leading step to lead the fiber bundle taken off in the unwinding step to the winding step between the unwinding step and the winding step, wherein the leading step or the winding step includes a resin adhesion operation to impregnate the fiber bundle with a resin, and the winding step includes a fiber content calculation operation to calculate a fiber content V f in % in a layer of the resin-impregnated fiber bundle being rolled up on the winding core of an intermediate product to control any one of (i) to (iv) according to the fiber content V f in %: (i) a resin adhesion amount in the resin adhesion operation; (ii) a winding tension of the fiber bundle applied to the intermediate product; (iii) a removal amount of a surplus resin layer generated on an outer surface of the intermediate product; and (iv) a resin viscosity in the intermediate product, (i) a resin adhesion amount in the resin adhesion operation; (ii) a winding tension of the fiber bundle applied to the intermediate product; (iii) a removal amount of a surplus resin layer generated on an outer surface of the intermediate product; and (iv) a resin viscosity in the intermediate product, wherein the winding step further includes a resin-impregnated fiber bundle layer thickness calculation operation to calculate a thickness t FRP of the layer of the resin-impregnated fiber bundle and then the fiber content calculation operation is performed by using the thickness t FRP, characterized in that the winding step further includes an outer diameter measurement operation to measure an outer diameter of the winding core or the intermediate product, and the thickness t FRP of the layer of the resin-impregnated fiber bundle, formed between a first time t 1 and a second time t 2 later than first time t 1, is calculated by using: a first outer diameter d 1 of the winding core or the intermediate product at the first time t 1; and a second outer diameter d 2 of the winding core or the intermediate product at the second time t 2, the first and second outer diameters d 1 and d 2 being measured by the outer diameter measurement operation.