A bill acceptor comprising: an acceptor housing comprising a base, a bill-inlet passage defined in said base for receiving a bill inserted by a user, a bill-outlet passage defined in said base and extended upwardly from a rear end of said bill-inlet passage, the bill-inlet passage being backwardly extended from a bill-inlet slot and the bill-outlet passage being backwardly extended from a bill-outlet slot, a bill-transfer mechanism mounted in said base for transferring said bill through said bill-inlet passage for said bill intake or said bill return and also for transferring said bill through said bill-outlet passage for giving change, and a bill-presser mounted in said base below said bill-transfer mechanism; a cash box comprising a box body mounted at a rear bottom side of said base of said acceptor housing and defining therein a bill accommodation chamber for receiving said bills being pressed by said bill-presser; and a bill dispenser comprising a dispenser housing mounted at a top side of said base of said acceptor housing, a bill-return passage defined in said dispenser housing in communication with said bill-inlet passage and said bill-outlet passage, a storage module mounted in said dispenser housing, said storage module comprising a first bill-receiving wheel facing toward said bill-return passage, a register module mounted in said dispenser housing, said register module comprising a second bill-receiving wheel facing toward said bill-return passage, and a control gate mounted in said dispenser housing and biasable to open and close a bill passage between said storage module and said register module; wherein said bill dispenser is adapted for performing a bill-collection process and a giving-change process selectively; when performing said bill collection process, said bill-transfer mechanism is controlled to transfer said bill from said bill-return passage to said storage module for enabling the said bill to be rolled up onto said first bill-receiving wheel; when performing said giving-change process, said first bill-receiving wheel is controlled to transfer said specific bills from said mixed bills through said bill-return passage into said bill-outlet passage for giving change to the user, enabling said bills coming before said specific bills to be transferred over said control gate into said register module and rolled up onto said second bill-receiving wheel for temporary storage and then delivered back to said storage module for storage after completion of the procedure of giving change. an acceptor housing comprising a base, a bill-inlet passage defined in said base for receiving a bill inserted by a user, a bill-outlet passage defined in said base and extended upwardly from a rear end of said bill-inlet passage, the bill-inlet passage being backwardly extended from a bill-inlet slot and the bill-outlet passage being backwardly extended from a bill-outlet slot, a bill-transfer mechanism mounted in said base for transferring said bill through said bill-inlet passage for said bill intake or said bill return and also for transferring said bill through said bill-outlet passage for giving change, and a bill-presser mounted in said base below said bill-transfer mechanism; a cash box comprising a box body mounted at a rear bottom side of said base of said acceptor housing and defining therein a bill accommodation chamber for receiving said bills being pressed by said bill-presser; and a bill dispenser comprising a dispenser housing mounted at a top side of said base of said acceptor housing, a bill-return passage defined in said dispenser housing in communication with said bill-inlet passage and said bill-outlet passage, a storage module mounted in said dispenser housing, said storage module comprising a first bill-receiving wheel facing toward said bill-return passage, a register module mounted in said dispenser housing, said register module comprising a second bill-receiving wheel facing toward said bill-return passage, and a control gate mounted in said dispenser housing and biasable to open and close a bill passage between said storage module and said register module; wherein said bill dispenser is adapted for performing a bill-collection process and a giving-change process selectively; when performing said bill collection process, said bill-transfer mechanism is controlled to transfer said bill from said bill-return passage to said storage module for enabling the said bill to be rolled up onto said first bill-receiving wheel; when performing said giving-change process, said first bill-receiving wheel is controlled to transfer said specific bills from said mixed bills through said bill-return passage into said bill-outlet passage for giving change to the user, enabling said bills coming before said specific bills to be transferred over said control gate into said register module and rolled up onto said second bill-receiving wheel for temporary storage and then delivered back to said storage module for storage after completion of the procedure of giving change.