The object of the present invention is to provide an actuator possible to transmit an output from a power rod of the actuator as rotary motion, and to provide an exhaust brake unit using the actuator, easy to assemble, a small space necessary for installation, able to place the actuator in such a manner that an axis of a power rod of the actuator and an axis of a valve shaft are aligned in a line, and heat transfer from an exhaust channel to the actuator is minimized. The exhaust brake unit is provided with a diaphragm 5 fixed between a first cover and a second cover, dividing into a first room and a second room, a retainer 6 fixed to the diaphragm, a spring 7 installed between the first cover and the retainer 6 or between the second cover and the retainer, a power rod 8 inserted in a movable manner to a concave portion of the retainer 6, a helical groove 8a formed on the outer peripheral surface of the power rod 8, and a protrusion 9 formed on a side wall of the retainer 6 protruding toward the concave portion and having the top end portion inserted into the groove. The top portion of the power rod 8 is connected to a valve shaft 22 of an exhaust gas control valve provided with a butterfly type valve 24 arranged in such a manner that it can open and shut a passage in the exhaust channel, through a lying-U shape connecting member 11.