PURPOSE: To provide a self-scanning checkout device which can easily and accurately notify a cashier of the fact that the commodities which are supposed to be hot registered yet are put into a cage of the downstream side regardless of the favorable or unfavorable self-scanning state or the presence of an evil intention.

CONSTITUTION: This checkout device is provided with the passage detector means 35A and 35B which are placed between the fixed scanners 21A and 21B and the registered commodity placing tables 3A and 3B, the commodity weight change detector means 40A and 40B which are provided on the tables 3A and 3B, and an error signal output control means. In such a constitution, an error signal is outputted when the passage of commodities are not detected by the means 35A and 35B although the weight change of commodities that are placed on the tables 3A and 3B are detected by the means 40A and 40B in the lanes 1A and 1B respectively. The means 40A and 40B are also provided on the unregistered commodity placing tables 2A and 2B.