PURPOSE: To provide a change gear operating mechanism of a small size which can detect a selection position accurately by arranging a magnet facing a set of hole sensors in such a way that it will never face any other hole sensor.
CONSTITUTION: Hole sensors 14 through 17 arranged in parallel in a casing face magnets 18 and 19 imbedded in a selection rod 1. In this case, let the hole sensors 14 and 15 be a A group, and let the hole sensors 16 and 17 be a B group, when the magnet 18 faces the hole sensor 14, the magnet 19 is arranged at the middle between the hole sensor 16 which is at the extreme tip point of the B group, and the hole sensor 15 which is at the extreme end point of the A group. In this constitution, only one hole sensor is subjected to magnet force from the magnet whereby the detected signal can be outputted. In addition, even if the selection space is shortened, as the hole sensor can be arranged, a gear shifting mechanism of a small size can be employed.