Abstract: A bill acceptor includes a bill acceptor body defining therein a bill passage, a bill slot panel mounted on the front side of the bill acceptor body and defining a bill insertion slot for the insertion of a bill into the bill passage, a bill box located on the rear side of the bill passage, a transmission mechanism for transferring an acceptable bill through the bill passage toward the bill box, a bill recognition unit for checking the authenticity and face value of an inserted bill, a bill pressing device for pushing each acceptable bill away from the bill passage into the inside of the bill box, two first adjustment devices for mounting on two opposite lateral sides of the bill passage to adjust the width of the bill passage to one of a set of bill passage widths, and two second adjustment devices for mounting on the inside of the bill slot panel at two opposite lateral sides relative to the bill insertion slot to adjust the width of the bill insertion slot subject to the bill passage width defined by the f