PURPOSE: To check on abnormality of a digital output generating circuit by storing a storage device with a steady value in normal operation, and comparing the stored value with an output value.

CONSTITUTION: Weight is detected by a load cell 1, amplified by an amplifier 3, and converted by an analog-digital converter 4 to display the weight on a display part 6, When the digital output generating circuit is checked, changeover switches 2 and 5 are operated. A power source 7 is connected to a fixed bridge 8, whose output voltage is inputted to a comparator 10 through the amplifier 3 and A/D converter 4. When the circuit is normal, the stored value of the storage part 9 where the output voltage of the fixed bridge 8 is stored is inputted to a comparator 10 to make a check, and an abnormality signal A is outputted when the difference is larger than a permissible value.