PURPOSE: To charge with compressed air only once so that it can be used in fifty or sixty times of work, by charging an air tank with compressed air with a pressure increased through a pressure increasing valve from an air supply source, and supplying charged compressed air with a pressure reduced through a pressure reducing valve to an actuator.

CONSTITUTION: This air tank unit is formed in a manner wherein a mechanical valve 5 operated by a manual switch 51 is connected to an actuator, to supply compressed air in an air tank 2 with a pressure reduced through a pressure reducing valve 21 to the actuator when the mechanical valve 5 is opened by operating the switch 51. Accordingly, when this unit is formed compact, in the case of generating necessity for supplying compressed air to an equipment with the compressed air serving as a drive source, when the unit is brought into a part where this equipment is provided, the compressed air can be very easily supplied to this equipment. Further in the case of charging with compressed air, since its charge is performed in a plant by very easy work from many arranged air supply sources, work efficiency can be improved.