To provide a deviatively placed load error preventive method of a leaf spring type weight sensor.

Both end parts of a plate-like metallic elastic material are formed as fixing parts 7 to constitute a roberval's mechanism by fixing upper and lower leaf springs 1, and parts from which a material is reduced and which have small elasticity, are adjacently formed in the fixing parts 7, and are formed as deflective parts 6 of the leaf springs 1, and a reinforcing member 8 is installed at a right angle to the lengthwise direction of the leaf springs 1 in a central part of a beam part 2 of the leaf springs 1 on which a nondeflective part sandwiched by both deflective parts 6 is formed as the beam part 2, and the leaf springs 1 are reinforced. In the reinforcing member 8 to further reduce deflection of the nondeflective part, a width of a contact part to the leaf springs 1 is formed in the minimum size necessary to install the reinforcing member 8 by a rivet, a screw or the like. A width of the reinforcing member 8 is formed in the minimum size by which a head part of the rivet, the screw or the like is stabilized and which is necessary to install the reinforcing member 8. A length of the reinforcing member 8 is set in a length slightly shorter than a width of a plane part of the beam part 2 of the leaf springs 1.