Abstract: An engine 2, a reduction gear 3, and a clutch 4 detachably coupling a reducing input shaft 25 of the reduction gear 3 to an engine output shaft 24, are housed in and supported to a support and frame work 1. A reducing output shaft 26 of the reduction gear 3 is used for a power takeoff shaft of the drive unit, and an input shaft of a work machine is coupled the power takeoff shaft, so that the work machine is operated. A weight of the support and frame work 1 is made smaller than a total weight of the engine 2, the reduction gear 3 and the clutch 4 so as to decrease a weight of unit. Thus, an over-loading can be overcome easily by using a friction clutch for the clutch 4.