The social infrastructures in Japan were intensively constructed during a period of high economic growth, and they are expected to rapidly deteriorate in the future. In this context, a thermoplastic carbon fiber reinforced plastic (CFRP) sheet adhesion method was developed for reinforcement, featuring flexibility and high adhesiveness characteristics. Thermoplastic resin is used as the base material of CFRP. The thickness of a thermoplastic CFRP sheet is approximately 0.25 mm, which enables storage in rolls and layered joint construction. In addition, using plasma surface treatment technology, the intermolecular forces with the epoxy adhesive resin were improved, enabling sheet-to-sheet joints. In this study, static loading tests on reinforced concrete (RC) beams were conducted to investigate the adhesion performance of thermoplastic CFRP sheets as flexural reinforcements bonded to RC beams. Experiments were conducted on five specimens by varying the type of bending reinforcement sheet and adhesive resin, and the presence and position of lap joints. The following results were obtained. (1) The adhesion of thermoplastic CFRP sheets can be expected to have a reinforcing effect same or greater than that of conventional carbon fiber sheets. (2) Even when the lap joints of the thermoplastic CFRP sheets are located where the maximum tensile stress and out-of-plane deformation occur owing to the shear force, a reinforcing effect equivalent or superior to that of the case without lap joints can be expected. (3) The interfacial delamination energy Gf is sufficiently larger than the design value Gfd (=0.5 N/mm) listed in the FRP Guidelines published by JSCE.