A sliding device for use with a variety of machines is reduced in overall length, thereby being compact in construction. The sliding device has a drive train enclosure made airtight and is acceptable for use in a clean environment. The sliding device includes an elongated sliding unit enclosure of airtight construction, a sliding table and a driving motor that is coupled to the drive train enclosure in parallel with the sliding unit enclosure. The drive train enclosure receives a drive train to carry power from the driving motor to the sliding table. The drive train enclosure is mounted with the driving motor while maintaining airtightness.