PURPOSE: To enhance weighing accuracy by providing a magnetic system allowing the predetermined max. holding force to act on a rotor in the direction opposite to the rotary direction of the rotor.

CONSTITUTION: The rotor 5 freely rotated around a horizontal rotary axis 4 is housed in a housing 1 and a plurality of holding means allowing the predetermined max. holding force to act on the rotor 5 in the direction reverse to the rotary direction of the rotor 5 are provided. This holding means are constituted of four permanent magnets 20 attached to the plate 19 fixed to the housing 1 at a right angle to the rotary axis of the rotor 5 and four permanent magnets 21 fixed to the disc 17 of the rotor 5. When a substance to be weighed is supplied into the small chambers 10 of an impeller 6 from a supply port 2, the rotor 5 is ready to rotate in the direction shown by an arrow 18 but this rotation is prevented by the holding forces of the magnets 20, 21. However, if the supply of the substance is continued, the wt. of the substance exceeds the holding forces acting on the rotor 5 at a certain point of time and the rotor 5 is rotated. As mentioned above, the rotor 5 is rotated only by the wt. of the substance in the small chambers 10 and weighing accuracy can be enhanced.