To miniaturize a drive unit and a neighborhood to the drive unit by arranging a wet type brake part in a space formed at an inner side of a second gear provided in a drive case and to facilitate adjustment of operation of the wet type brake by providing pressing out mechanism part for operating a service brake and a parking brake wet brake and providing an operation adjustment part of the wet brake.

The space is formed at the inner side of the second gear 13 provided in the drive case 2 and the wet type brake part 31 is arranged at the space. The wet type brake part 31 is constituted by an inner disc 32 having the whole periphery of an inner periphery mounted to the second gear 13; an outer disc 33 having the whole periphery of an outer periphery mounted to the drive case 2 side opposed to the inner disc 32; and a pressure plate 34 for pressing the inner disc 32 and the outer disc 33 opposed to each other.