A bicycle frame structure having a rear frame and a front frame includes a rear frame of which a left stay and a right stay are bonded to each other, and an insert portion is formed at a bonded end portion, and a front frame where a head tube is formed at a front end portion thereof, an insertion hole into which the insert portion is inserted is formed at a rear end portion thereof, and the front frame is bonded to the rear frame along the circumference of the insertion hole.