An optical-fiber-spliced portion reinforcing heating device comprising: a pair of right and left clamps arranged to respectively grasp one portion and the other portion of a coated portion of an optical fiber, the optical fiber including a fusion-spliced portion, the fusion-spliced portion being coated with a sleeve, the coated portion being exposed from the sleeve, where optical fibers are fusion-spliced at which the coated portion is removed and a coating-removed portion of a fusion-spliced portion and the coated portion of the optical fibers are covered with the sleeve; at least two or more heaters that are arranged to face each other so as to sandwich the sleeve; a first force-applying member that is arranged to cause at least one of the paired right and left clamps to slidably move in a longitudinal direction of the optical fiber so as to apply a tension to the optical fiber by use of one of an elastic member and a magnetic member; and a second force-applying member that is arranged to apply a pressing force to at least one or more of the heaters via the sleeve in accordance with control of a drive source, the heaters being arranged to face each other with the sleeve interposed therebetween, wherein a pressing force that is to be applied to the sleeve by the second force-applying member is set to be greater than a tension that is to be applied to the optical fiber by the first force-applying member, the first force-applying member arranged to grasp one of the right and left clamps while pressing one of the right and left clamps in a state where movement of one of the right and left clamps the longitudinal direction of the optical fiber is restricted by the first force-applying member, thereafter, restriction of movement is arranged to be released, therefore, in a state in which a tension is applied to the optical fiber, one of the right and left clamps is configured so that a backward movable range in a direction away from the heaters in the longitudinal direction of the optical fiber is ensured, a forward movable range that allows movement to the heater side is ensured, and one of the right and left clamps is thereby configured to move in a direction in which a tension that is applied to the optical fiber as a result of pressing the sleeve by the heaters and by the second force-applying member is diminished. a pair of right and left clamps arranged to respectively grasp one portion and the other portion of a coated portion of an optical fiber, the optical fiber including a fusion-spliced portion, the fusion-spliced portion being coated with a sleeve, the coated portion being exposed from the sleeve, where optical fibers are fusion-spliced at which the coated portion is removed and a coating-removed portion of a fusion-spliced portion and the coated portion of the optical fibers are covered with the sleeve; at least two or more heaters that are arranged to face each other so as to sandwich the sleeve; a first force-applying member that is arranged to cause at least one of the paired right and left clamps to slidably move in a longitudinal direction of the optical fiber so as to apply a tension to the optical fiber by use of one of an elastic member and a magnetic member; and a second force-applying member that is arranged to apply a pressing force to at least one or more of the heaters via the sleeve in accordance with control of a drive source, the heaters being arranged to face each other with the sleeve interposed therebetween, wherein a pressing force that is to be applied to the sleeve by the second force-applying member is set to be greater than a tension that is to be applied to the optical fiber by the first force-applying member, the first force-applying member arranged to grasp one of the right and left clamps while pressing one of the right and left clamps in a state where movement of one of the right and left clamps the longitudinal direction of the optical fiber is restricted by the first force-applying member, thereafter, restriction of movement is arranged to be released, therefore, in a state in which a tension is applied to the optical fiber, one of the right and left clamps is configured so that a backward movable range in a direction away from the heaters in the longitudinal direction of the optical fiber is ensured, a forward movable range that allows movement to the heater side is ensured, and one of the right and left clamps is thereby configured to move in a direction in which a tension that is applied to the optical fiber as a result of pressing the sleeve by the heaters and by the second force-applying member is diminished.