PURPOSE: To provide a double acting tandem hydraulic actuator having an coincident diameter and capable of doubling driving force.

CONSTITUTION: A double acting tandem hydraulic actuator has a longitudinal line cylinder 4a formed by partitioning a cylinder both ends of which are closed into a lateral pair of cylinder chambers 6L, 7R by a central bulkhead 16; a common piston rod 17 liquid-tightly extending through the central bulkhead 16 and the outer end of at least one cylinder chamber in such a manner as to be capable of sliding; a lateral pair of pistons 5L, 6R fitted into the cylinder chambers 6L, 7R, respectively and fitted to the common piston rod 17; and oil pressure branching pipes 11L, 11R, 12L, 12R for connecting oil pressure supply conduits 2, 3 from a spool valve 1 in parallel to the cylinder chambers 6L, 7R respectively.