Abstract: An oscillator is proposed which comprises a pair of cylinders having a common, circular-cylindrical outer wall (100) and two sealingly guided pistons (120, 122) each having one piston rod (121, 123), which are likewise guided in a sealing manner to the outside through the closure walls of the cylinder. The cylinder is divided by the pistons (120, 122) into outer chambers (124, 125) and inner chambers combined into one common chamber (126). The chamber (126) is filled with fluid. The outer chambers (124, 125) have two openings (102, 103) offset from one another by 180.degree.. A control cylinder (101) having axially offset, oppositely disposed holes (104, 105, 106, 107) connects the outer chambers in alternation with an annular high-pressure chamber (113, 115) and an equalization chamber (114) whenever the control cylinder (101) is rotated. The two pistons (120, 122) thereby execute movements in common toward the left or right, respectively.