A solenoid actuator (1) attached to a hydraulic equipment comprises a shaft (5) connected to the hydraulic equipment, a plunger (4) fixed to the shaft (5), a coil (12) which magnetically drives the plunger (4), and a first bearing (7) and a second bearing (8) supporting the shaft (5) on both sides of the plunger (4). A plunger front chamber (74) is formed between the first bearing (7) and the plunger (4), a plunger rear chamber (75) is formed between the plunger (4) and the second bearing (8), and a second bearing rear chamber (76) is formed on the opposite side of the second bearing (8) to the plunger rear chamber (75). To secure an oil flow between these chambers, a plunger exterior oil passage (63), a second bearing oil passage (64), and a shaft-penetrating oil passage (65) are provided, thereby realizing a preferable balance between oil pressures acting on the second bearing (8).