Abstract: A rotary actuator for converting a linear reciprocatory movement of a piston into a rotary reciprocatory movement of an output shaft through a connecting member. The rotary actuator includes a cylinder case formed with a pedestal in a position in which the output shaft extends vertically out of the cylinder case. The pedestal is formed with a substantially square elevated portion, and a depressed portion defined by the elevated portion. A plurality of projections spaced apart from each other by a predetermined angle are formed integrally with the pedestal in the depressed portion to constitute dividing lines of a scale for indicating the angle of rotation of the output shaft by means of a pointer.