To provide a rotary actuator which can enlarge a guide passage for passing tubing or wiring without increasing the whole size.

A cylindrical cylinder tube 18 is installed so that its axial line may be on one circumference. Both the ends of the cylinder tube 18 are locked by end blocks 14, 15, and a piston 25 which is capable of moving along the cylinder tube is stored in the cylinder tube 18. By supplying and discharging pressure fluid through supplying/discharging ports 21, 22 formed at the end blocks 14, 15, a piston 25 moves, and a traveling element 29 is moved, following the movement. A table is fixed at the traveling element 29, and rotates itself with the movement of the traveling element 29. A guide passage 8 whose diameter is large is formed in the middle of the table, and tubing or wiring extending from respective driving devices on the table is introduced in the guide passage 8.