To reduce the magnetic resistance of a magnetic path surrounding a coil of a solenoid actuator.

An armature 52 is movably disposed in a notch of a magnetic path forming member comprising an actuator case 13, a third elastomer support ring 16 and a fixing core 42 disposed to surround the cylindrical coil 44 wound around an axial line L in the axis direction L. A magnetic fluid 53 having magnetic permeability higher than air is disposed between a gap g2 for receiving magnetic flux out of a gap g1 for suction formed between the armature 52 and the fixing core 42, and a gap g2 for receiving the magnetic flux formed between the armature 52 and the third elastomer support ring 16. Thereby, the magnetic resistance of the gap g2 for receiving the magnetic flux can be reduced. The working responsibility of the actuator 41 and an output of the actuator can be increased while suppressing the electric power consumption of the coil 44.

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