A fusion splicer includes an imaging unit configured to take a lateral transmission image by illuminating a target optical fiber from a lateral direction of the target optical fiber; a determination module configured to create a target luminance distribution in a direction perpendicular to an optical axis of the target optical fiber using the lateral transmission image so as to determine a type of the target optical fiber, by comparing the target luminance distribution with preliminarily registered data of a reference luminance distribution of a reference optical fiber; and a registration module configured to create a message when the target luminance distribution is determined to be outside a tolerance of the reference luminance distribution and to display the message to an operator so that the operator can decide whether or not to register the target luminance distribution of the target optical fiber as a new reference luminance distribution.