Disclosed is a constant voltage power supply, which comprises an error amplifier VEA including a transistor M3, and a transistor M4 having the same ratio between channel width and channel length as that of the transistor M3. The injector has a drivable piezo-actuator. Preferably this check stand has an output module which has two belts and two rollers so that the check stand can use a bagger on each side for bagging the items, to speed checkout time. Based on the change in WOB, the excavating system is adjusted so the realized WOB approximates the target WOB. According to this configuration, mechanical strength of the frame and its producibility are maintained, and cogging torque caused by magnetic-circuit distortion in an iron core generated due to the frame shape is also reduced.