According to the measuring head, the zero point and the amount of front travel settings are facilitated. In one embodiment a laryngoscope blade includes a main blade portion and blade tip and a blade base. The shaft has a plurality of outer teeth protruding outwardly from an outer surface of a top end thereof. Thus, current of the lamps included in the closed loop is made uniform, and also current is made uniform even between the closed loops by connecting the primary windings of the transformers serially.