An oil sealing structure of an output spindle of a deceleration device of an industrial robot is provided to couple an oil seal case to a lower end of a deceleration case by using a bolt while surrounding the output spindle and to form another oil seal between a receiving part and an attachment formed at the lower end of the oil seal case. A second oil seal(32) is provided at the lower end portion of a case(21) of a deceleration device equipped with a first oil seal(22) so that lubricant leaked due to the abrasion of the first oil seal is shielded by the second oil seal. An oil seal case(31) is coupled to a lower end of the case by using a bolt(36). The second oil seal is additionally provided between the lower end of the oil seal case and an attachment(30). The oil seal case is provided at the lower end thereof with a receiving part(34) to receive the second oil seal.
