To provide a simple and compact speed selecting mechanism by eliminating a corotation type bearing causing fretting corrosion in a conventional method, in a speed-selecting mechanism housed in a gear-type speed increasing and decreasing device.

An input shaft is arranged so as to be included in an independent hollow shaft pinion supported at both ends, an independent solid pinion having the different number of tooth and supported at both ends is arranged on the extension of an axis of the input shaft, a selecting clutch is engaged and arranged between them by the input shaft and a slidable spindle, the selecting clutch is slid, to be attached to and detached from the hollow shaft pinion or the solid pinion, so as to enable speed switching.