Driving device for a watercraft, which device comprises a water flow channel (10) which is connected to the watercraft, preferably to the bottom thereof, and which has an inlet (11) and an outlet (12), a drive shaft (13, 14) which extends into said channel (10), a bearing shaft (15) coaxially arranged with the drive shaft part (14) in said channel, a first rotating impeller (21) connected to the drive shaft (13) for rotation in said channel (10) for the movement of water in either direction between the inlet (11) and the outlet (12), a second impeller (22) which is contra-rotating to the first impeller (21) and connected to the bearing shaft (15) for rotation in said channel (10) for the movement of water in said direction between the inlet (11) and the outlet (12), and that the drive shaft (13, 14) and the bearing shaft (15) are connected to each other via a planetary-like gearing (30), wherein one of said impellers (21, 22) is formed with an impeller casing (31) which is provided with an outer surface (322) and inside which, said gearing (30) is situated.