PURPOSE: To make an automatic span adjustment and to improve availability by mounting an inspection weight on a load detection part at a proper period during use.

CONSTITUTION: A body whose weight is already known is mounted on the load detection part 20 and a multiplier 46 multiplies a weighing signal generated by the detection part 20 by a predetermined span coefficient to make the span adjustment. This span coefficient is set by memories 48 and 50, changeover switches 52 and 54, a readout part 56, a comparison part 58, a normally open switch 60, and a divider 62. Then, it is decided whether or not there is variation larger than the predetermined value between the span-adjusted weighing signal and the previously stored weight of the body. Then when it is decided that there is the variation, a span coefficient is calculated automatically and newly by using the original weighing signal of the detection part 20 and the stored weight of the body. Then, a span adjustment is made thereafter by using the newly calculated span coefficient.