ELECTRIC SPEEDOMETER

PURPOSE:To prevent the generation of a lock state due to the running-on of the helical gear of a worm gear by providing a slip mechanism for engaging the worm gear with a revolving shaft with respect to the rotation in one direction of the revolving shaft of a pulse motor, and also releasing the engagement when rotational force exceeding prescribed rotational force is applied in the other direction to the revolving shaft. CONSTITUTION:When the pulse motor 10 is reverse rotated forcibly, and pressure between the tooth 29a of the worm gear 29 and the tooth 3a of the helical gear 3 becomes large, the worm gear 29 compresses a coil spring 31 against the spring force of the coil spring 31, following the rotation of the revolving shaft 22 and moves in the direction as indicated with an arrow C. As a result, the end face 29c of the worm gear 29 is separated from a stopper collar 27. Also, the end face 29d of the worm gear 29 and a stopper collar 28 are also separated, the engagement relation of the worm gear 29 and the revolving shaft 22 of the pulse motor 10 by frictional force of the coil spring 31 is released, the worm gear 29 becomes slippable against the two stopper collars 27, 28, namely, the revolving shaft 22, only the revolving shaft rotates, and the pulse motor 10 is rotated by a full scale to stop thereafter.