The purpose of the present invention is to provide a carbon fiber bundle for resin reinforcement purposes, which is produced using a sizing agent that can exert satisfactory interface adhesiveness to both of a carbon fiber bundle and a thermoplastic resin in the production of a carbon-fiber-reinforced thermoplastic resin, and which has satisfactory emulsion stability. One embodiment of the present invention is a carbon fiber bundle for resin reinforcement purposes, which comprises a carbon fiber bundle and a polymer adhered onto the carbon fiber bundle, wherein the polymer is produced by binding an acid-modified polyolefin having a polyolefin structure and an acidic group in the molecular structure thereof to a hydrophilic polymer having a weight average molecular weight (Mw) of 450 or more, and wherein the ratio of the mass of the polyolefin structure to the mass of the acidic group in the acid-modified polyolefin is 100:0.1 to 100:10, the ratio of the mass of the acid-modified polyolefin to the mass of the hydrophilic polymer is 100:1 to 100:100, and the content of the polymer in the carbon fiber bundle for resin reinforcement purposes is 0.1 to 8.0 mass % inclusive.