An optical fiber reinforcing heating device has a base part, to which a first lid part for covering a sleeve accommodation groove for containing a fiber reinforcement sleeve covering a fusion-splicing part of optical fibers is attached so as to be openable and closable. A pair of fiber holders for holding and securing the optical fibers are disposed on both end sides of the first lid part. Each fiber holder has a second lid part which is attached to a fiber container so as to be openable and closable and presses the optical fiber against the fiber container. A switch lever which is movable longitudinally of the sleeve accommodation groove is disposed on the upper face of the second lid part built in with a pin adapted to move in conjunction with the switch lever. A joint hole adapted to engage the pin is formed within the first lid part.