A bill transaction system for tracing counterfeit bank notes including an ATM for deposition of bank notes by a user, a tracing terminal device including a search engine for tracing a user who deposited a counterfeit bank note, and a database, - said ATM comprising a validator including an optical sensor and optionally magnetic sensor to obtain optical and optionally magnetic characteristics of bank notes deposited in said ATM, said validator being configured to judge bank notes deposited in the ATM as genuine bank notes or counterfeit bank notes or doubtful banknotes by determining whether or not the optical and optionally magnetic characteristic of the banknote is within an allowable range, and to judge a denomination of said bank notes deposited in said ATM; - a storage safe box for stacking bank notes deposited in said ATM and judged as counterfeit bank notes or as doubtful by the validator to separate and hold bank notes which have been judged as counterfeit bank notes or as doubtful by the validator; - said database including a search database for storing, for a plurality of doubtful and counterfeit bank notes deposited in said ATM, as a search data set of a deposited doubtful or counterfeit bank note, an optical characteristic of said deposited bank note obtained by the optical sensor of the validator together with information specific to the user when the respective banknote is deposited in said ATM for a first time by a user; - said database further comprising a trace database for storing, as a trace data set of one of said doubtful bank notes, after it had been verified as being a counterfeit bank note at a center outside the ATM, or one of said counterfeit bank notes, an optical characteristic obtained by the optical sensor of the validator from said one bank note, which had already been deposited for a first time in said ATM, and for which search data set exists in said search database, after said one bank note is deposited in said same ATM for a second time, wherein said search engine is configured to compare a trace data set of a specific bank note stored in said trace database with a plurality of search data sets stored in said search database to determine a degree of similarity of an optical characteristic of said bank note stored in said trace data set with an optical characteristic of a bank note stored in one of said search data sets to re-identify a specific bank note, which had been deposited in said ATM already at a first time and which has been judged by the validator as a doubtful or a counterfeit bank note, and to trace a user based on the resulting degree of similarity by retrieving an information specific to a user from the search data set with the highest degree of similarity. - said ATM comprising a validator including an optical sensor and optionally magnetic sensor to obtain optical and optionally magnetic characteristics of bank notes deposited in said ATM, said validator being configured to judge bank notes deposited in the ATM as genuine bank notes or counterfeit bank notes or doubtful banknotes by determining whether or not the optical and optionally magnetic characteristic of the banknote is within an allowable range, and to judge a denomination of said bank notes deposited in said ATM; - a storage safe box for stacking bank notes deposited in said ATM and judged as counterfeit bank notes or as doubtful by the validator to separate and hold bank notes which have been judged as counterfeit bank notes or as doubtful by the validator; - said database including a search database for storing, for a plurality of doubtful and counterfeit bank notes deposited in said ATM, as a search data set of a deposited doubtful or counterfeit bank note, an optical characteristic of said deposited bank note obtained by the optical sensor of the validator together with information specific to the user when the respective banknote is deposited in said ATM for a first time by a user; - said database further comprising a trace database for storing, as a trace data set of one of said doubtful bank notes, after it had been verified as being a counterfeit bank note at a center outside the ATM, or one of said counterfeit bank notes, an optical characteristic obtained by the optical sensor of the validator from said one bank note, which had already been deposited for a first time in said ATM, and for which search data set exists in said search database, after said one bank note is deposited in said same ATM for a second time,