A method of producing a partially separated fiber bundle includes a partial separation processing step for alternately forming separation-processed sections, each divided into a plurality of bundles, and not-separation-processed sections along the lengthwise direction of a fiber bundle, wherein a separation means provided with a plurality of projected parts is penetrated into the fiber bundle to create separation-processed parts, the separation means is removed from the fiber bundle, and the separation means is penetrated into the fiber bundle again, characterized in that a sizing agent is applied at an arbitrary timing during the production process of the partially separated fiber bundle. A partially separated fiber bundle is obtained by the production method, a fiber-reinforced resin molding material uses the partially separated fiber bundle, and a production method makes the fiber-reinforced resin molding material.