To provide a throttle actuator to increase an operation speed, be excellent in durability, and reduce a cost.

A hydraulic motor type throttle actuator 20 comprises mainly a hydraulic motor part 20b, a rotor 20c, and a solenoid 20d. The hydraulic motor part 20b is provided in a case body 55 with a plurality of fan-shaped hydraulic chambers, pistons 57a and 57b, connected to the throttle shaft 5c of a throttle valve 5a, respectively, are rotatably inserted in the respective hydraulic chambers, and oil feed chambers 55g and drain chambers 55h are alternately formed. Further, a rotor 20c is formed such that a rotary valve 58 is rotatably inserted in the central part of the case body 55 and a magnet 59 is securely mounted on a valve shaft 58a. A solenoid 20d is constituted such that a lamination core 62 is disposed opposite to the magnet 59 and an exciting coil 63 is wound around the outer periphery of the lamination core 62.