WAVE GEAR DEVICE AND HOLLOW ROTATING ACTUATOR

An objective of the present invention is to provide a wave gear device in which a rigid boss and a bearing inner wheel of a flexible external tooth gear can be fixated by a simple configuration, and a reliable sealing can be provided therebetween. The wave gear device (3) has a rigid internal tooth gear (32), the flexible external tooth gear (33), a wave generator (34), a bearing (35) which supports the flexible external tooth gear (33) in a state capable of relative rotation with respect to the rigid internal tooth gear (32); and a first welding portion (38) where the rigid boss (33c) and the inner wheel (35b) of the bearing (35) of the flexible external tooth gear (33) are fixated. The first welding portion (38) is a whole circumference welding portion where the boss (33c) and the inner wheel (35b) are sealed in a liquid-tight state therebetween. The boss (33c) and the inner wheel (35b) have at least sufficient dimensions in an axial direction, and can be fixated to each other with little labor processing and labor assembly. The boss (33c) and the inner wheel (35b) can be sealed therebetween without using an oil seal.