An optical fiber fusion splicer (10, 10A to 10H) comprising: an apparatus body having a heat fusion portion that fusion-splices optical fibers; a windshield cover (60, 60A, 60B, 60C) that is formed so as to be openable and closable with respect to the apparatus body by one or more cover members (61, 61A, 62, 62A) and that covers the heat fusion portion in a closed state; clamp mounts or a pair of holder mounting portions that are provided on both sides of the heat fusion portion of the apparatus body; a coating clamp that holds a coated portion of the optical fiber between a lower clamp member fixed on the clamp mount and an upper clamp member pivotally attached to the lower clamp member so as to be openable and closable with respect to the lower clamp member, or a fiber holder that holds a coated portion of the optical fiber between a base plate and a lid member pivotally attached to the base plate so as to be openable and closable with respect to the base plate, the fiber holder being detachably placed on the holder mounting portion; characterised by fiber mounting detectors that are respectively provided in both of the clamp mounts or both of the holder mounting portions; a windshield open and close power source (63a, 63b) that is configured to open and close the windshield cover (60, 60A, 60B, 60C); and a driving control device that controls a driving of the windshield open and close power source (63a, 63b) based on detections of the fiber mounting detectors, wherein the fiber mounting detectors are configured to detect that the optical fiber has been mounted by detecting either one of that the upper clamp member of the coating clamp has been closed with respect to the lower clamp member, that the fiber holder has been mounted on the holder mounting portion, that the optical fiber has been placed on the lower clamp member of the coating clamp, and that the optical fiber held and fixed to the fiber holder has been disposed at a predetermined position on the holder mounting portion as optical fiber mounting, and when both of the fiber mounting detectors detect that the optical fibers have been mounted, the driving control device is configured to control the driving of the windshield open and close power source (63a, 63b) for closing the windshield cover (60, 60A, 60B, 60C) in a state where the windshield cover (60, 60A, 60B, 60C) is open, and for opening the windshield cover (60, 60A, 60B, 60C) after the connection portion inspection is completed. an apparatus body having a heat fusion portion that fusion-splices optical fibers; a windshield cover (60, 60A, 60B, 60C) that is formed so as to be openable and closable with respect to the apparatus body by one or more cover members (61, 61A, 62, 62A) and that covers the heat fusion portion in a closed state; clamp mounts or a pair of holder mounting portions that are provided on both sides of the heat fusion portion of the apparatus body; a coating clamp that holds a coated portion of the optical fiber between a lower clamp member fixed on the clamp mount and an upper clamp member pivotally attached to the lower clamp member so as to be openable and closable with respect to the lower clamp member, or a fiber holder that holds a coated portion of the optical fiber between a base plate and a lid member pivotally attached to the base plate so as to be openable and closable with respect to the base plate, the fiber holder being detachably placed on the holder mounting portion; characterised by fiber mounting detectors that are respectively provided in both of the clamp mounts or both of the holder mounting portions; a windshield open and close power source (63a, 63b) that is configured to open and close the windshield cover (60, 60A, 60B, 60C); and a driving control device that controls a driving of the windshield open and close power source (63a, 63b) based on detections of the fiber mounting detectors, wherein the fiber mounting detectors are configured to detect that the optical fiber has been mounted by detecting either one of that the upper clamp member of the coating clamp has been closed with respect to the lower clamp member, that the fiber holder has been mounted on the holder mounting portion, that the optical fiber has been placed on the lower clamp member of the coating clamp, and that the optical fiber held and fixed to the fiber holder has been disposed at a predetermined position on the holder mounting portion as optical fiber mounting, and when both of the fiber mounting detectors detect that the optical fibers have been mounted, the driving control device is configured to control the driving of the windshield open and close power source (63a, 63b) for closing the windshield cover (60, 60A, 60B, 60C) in a state where the windshield cover (60, 60A, 60B, 60C) is open, and for opening the windshield cover (60, 60A, 60B, 60C) after the connection portion inspection is completed.