An external device is configured to be detachably attached to a measuring instrument via a connector. The external device includes a connector part, an external device body part and a movable connection part. The connector part has a connection terminal. The external device body part has a display part on a side surface of the external device body part. The movable connection part is configured to connect the connector part with the external device body part. The movable connection part is a biaxial rotation hinge having two pivot axes which are in a twisted position relationship with respect to each other.