To provide a power transmission change-over mechanism which is inexpensive and simplified in structure.

The power transmission change-over mechanism comprises: a shaft 1 rotatably and slidably supported in right and left trestles 2, 3; a driving gear 5 of a first transmission system spur gear 4 slidably installed in one side of the shaft 1; and a driving gear 11 of a second transmission system spur gear 10 journaled to the other side of the shaft, and is comprised of: a coil spring 17 wound around the shaft between a spring seat 15 fixedly installed in the shaft 1 and the first driving system driving gear 4 between the first transmission system and the second transmission system driving gears; and a collar 21 slidably and loosely fitted in the shaft 1 so that the first driving system driving gear 5 is also moved as a handle 18 is moved between a handle 18 slidably installed in one side end of the shaft 1 and the first driving system driving gear 4. The shaft 1 is formed to such a length that the right end is projected from the right side trestle 3 a little.