A solenoid actuator (1) comprises a case (9) made of a magnetic material and housing a coil (12) wound on a bobbin (11), and a pressure tube (17) made of a non-magnetic material and fitted into a hollow portion of the bobbin (11). A base (2) and a sleeve (3) made of a magnetic material are disposed in the pressure tube (17). A plunger (4) provided in an operation chamber (74, 75) formed in the base (2) and the sleeve (3) strokes according to energization of the coil (12) to axially drive a shaft (5) fixed to the plunger (4). The pressure tube (17) ensures that magnetic flux is transferred between the case (9) and the sleeve (3) while preventing pressure variation in the operation chamber (74, 75) from being transmitted to the bobbin (11), thereby achieving a high response and a pressure tightness in the solenoid actuator (1).