Abstract: A hydraulic-pneumatic cylinder device of the invention comprises a tubular housing closed at both ends, and an actuating piston slidably guided in the housing and connected to a piston rod. A pair of hydraulic units, each of which comprises a pair of volume-variable liquid chambers in communication with each other through a flow control passage, are arranged within the housing on both sides of the piston to act thereon in opposite axial directions. A pair of air chambers, which are selectively connectable to an air supply source, are also provided within the housing to act on the respective hydraulic units. Operation of the cylinder device can be reliably adjusted by a flow regulating valve provided at each flow control passage.