To attain size reduction in a gear box, and provide the large speed reduction ratio by constituting a speed reduction mechanism of a driving means to drive a rotary wheel out of a planetary gear, and directly connecting this planetary gear, the rotary wheel and a driving source to each other.

A driving means 6 to drive a delivery rotary wheel 5 extending from a main body 16 is housed in the main body 16, and a speed reduction mechanism 13 is connected to the rotary wheel 5, and a driving source 17 composed of a hydraulic motor is connected to this speed reduction mechanism 13. The speed reduction mechanism 13 connected to its driving source 17 is constituted of a planetary gear mechanism, and in this planetary gear mechanism, a sun gear 18 is connected to the driving source 17, and a fixed gear 20 is meshed with this sun gear 18 through a planetary gear 19, an arm 21 is installed on the axis 01 of the planetary gear 19, and an output shaft 22 of this arm 21 is installed on the rotary wheel 5.