PURPOSE: To enable sure switching even to a stem in a high-speed rotation by enabling the generation of a modifying signal at a speed proportional to the rotational speed of the stem.

CONSTITUTION: When the stem is pulled out to a prescribed position and is rotated, the rotation thereof is transmitted to a switch wheel 30 through a switch transmission wheel, whereby a switch insulating seat 37, a movable switch plate 38 and movable contacts S4 and S5 are rotated at a high speed. By this rotation, the contacts S4 and S5 contact sequentially with fixed contacts S1WS3, closing the same. In this case, the movable contacts are two, while the fixed contacts are three, and they have no common divisor, no two sets of contacts are closed simultaneously and are set separetely so that they are closed sequentially in the normal or reverse direction. Accordingly, the control circuit can generate modifying signals in the normal and reverse directions, respectively and in proportion to the rotational speed of the stem. Therefore, by adjusting the rotational speed of the stem properly, the modification can be performed simply.