PURPOSE: To provide a speed controller which is compact, requires no lining, is easy in installation, and is used in both of a double acting and a single acting type or exclusively used in any one of them.

CONSTITUTION: Passages 3, 4 are parallelly provided on a main body 2 of a controller. Speed control mechanisms 6, 7 and 8 are provided with needle valves 8a, 7a, 8a and check valves 6b, 7b and 8b. The check valves 6b, 7b of the mechanisms 6, 7 are arranged so as to have reversed working directions, while the mechanisms 6, 7 are serially arranged in the first passage 3. The speed control mechanism 8 is arranged in the second passage 4. A closable bypass passage 5 is arranged between the first and the second passages 3 and 4, and thereby a speed controller of a pneumatic rotary actuator is obtained.