This vehicle body frame structure is provided with: a head pipe (21); a main frame (22) which extends to the rear of the head pipe (21); and a seat rail (30) which extends to the rear of the main frame (22). The main frame (22) and/or the seat rail (30) are/is provided with a curved part (37) that is curved when viewed from a first direction, and are/is formed by combining a plurality of press frame bodies (45I, 45O). The plurality of press frame bodies (45I, 45O) are provided with bulging parts (45bs) which form a closed section structure (30cs) when combined with each other. Joint parts (sp) which join the plurality of press frame bodies (45I, 45O) together are provided to joining flanges (45e) which extend from the bulging parts (45bs) of the press frame bodies (45I, 45O) to be joined. The distance from panel bent parts (45e5) from which the bulging parts (45bs) start, said panel bent parts being located at proximal ends of the joining flanges (45e), to the joint parts (sp) is longer in the curved part (37) than in general parts of the frame excluding the curved part (37).