A clean environmental actuator is less in weight, height in transverse section and compact in construction, even with ensuring accurate position control and conformable to high speed operation and high acceleration/deceleration. Both a bed and a slider are stowed in an enclosure and packings are in T-slots in side walls of the bed to seal clearances between the bed and the enclosure. The enclosure is composed of an end bracket to cover one end of the bed, a motor bracket to cover another end of the bed, a pair of side coverings to enclose the side surfaces and tops of the side walls of the bed, a sealing panel to cover an upward opening between the side coverings, and a table covering to overlay an area of the sealing panel lying on the slider and side areas of the table bulging out from side edges of the sealing panel.