PURPOSE: To make it needless to provide an annular groove on a conventional fixed support in a crawler-type driver, only by providing a floating seal which can seal up a driving sprocket from the fixed support.

CONSTITUTION: The crawler-type driver comprises the fixed support 5 which supports the driving sprocket 4 on a bearing 8 mounted on the support, a swash plate type hydraulic motor 9 installed in the fixed support 5, and a speed reducer 11 which transmits the rotation of the hydraulic motor 9 to the driving sprocket 4 while retarding the rotation. A tapered sealing hole 84 continuous to a hole 81 of the sprocket 4 is provided concentrically with the sprocket 4. The fixed support 5 is provided with a facing surface 88 which faces the sealing hole 84 across a gap. The annular floating seal 90 is fitted in the sealing hole 84 so that the fixed support 5 and the driving sprocket 4 are sealed up from each other.