Load reaction type speed change device

The utility model provides a load reaction type speed change device which is composed of a small number of parts and automatically changes speed in reaction with the load. The speed change device is provided with a planetary gear transmission system which is provided with the following components: a sun gear, a gear ring which surrounds the sun gear, planetary gears which is engaged with the sun gear and the gear ring, a planetary carrier which can perform revolution with the planetary gears, and an output system which outputs revolution of the planetary carrier. The speed change device is provided with a load acquiring unit which acquires quantity of the load that functions on the output system as an action amount on the machinery. The speed change device is provided with a switching unit which causes the sun gear, the gear ring, the planetary gears and the planetary carrier to rotate together when the load that is acquired by the load acquiring unit is smaller than a preset value. Furthermore when the load