PURPOSE: To reduce the vibration reaction of a motor-compressor unit by forming a stator into a W-shape, forming air gaps between their respective limbs and arranging a coupling between a piston and an armature on the side opposite to the magnetic pole element of the armature relative to a motor shaft.

CONSTITUTION: The only stator 2 of a vibration motor 1 is formed into a W- shape, and arcuate air gaps 9 and 10 are formed between each of the peripheral surfaces 6, 7 and 8 of the central limb 3, outer limbs 4 and 5. Coils 16 and 17 are wound around the outer limbs 4 and 5. The armature 11 made of permanent magnetic material is rotatably supported by a motor shaft 12 and is also radially polarized. The magnetic pole element 13 of the armature 11 is reciprocatable in the air gaps 9 and 10. When an alternating current is made to flow in the coils 16 and 17, the fluxes in the gaps 9 and 10 are alternatingly increased and decreased, vibrating the magnetic pole element 13 and in its turn the armature 11. Since the magnetic pole element 13 is positioned in the side directly opposite to a compressor side 21 relative to a shaft 12, their inner forces cancel each other without applying reaction to the shaft 12.