Provided with a sealed rotational output unit (3) which includes a tubular shaft (12) having an outer circumferential surface sealed with a ferrofluidic seal (13); a rotating output shaft (14) disposed inside the tubular shaft (12); and an O-ring (17, 18) that seals between the tubular shaft (12) and the rotating output shaft (14). When the rotating output shaft (14) is directly coupled to a hollow motor shaft (9), shaking thereof is absorbed by the O-ring (17, 18), causing no excessive stress to be produced on the bearing side of the hollow motor shaft (9) or on a bearing (15, 16) side of the ferrofluidic seal (13). Since the tubular shaft (12) rotates in conjunction with the rotating output shaft (14), the O-ring (17, 18) that seals therebetween does not degrade in sealing capability due to wear by sliding. The sealed rotational output unit can be used with high rotational accuracy by directly coupling to a hollow motor (2) without any joint.