An apparatus for discriminating valuable papers is provided wherein a validation control circuit 56 (i) drives conveyer device 8 to inwardly move bill along passageway 9 when inlet sensor 13 detects bill, (ii) ceases driving of conveyer device 8 to keep bill in the standby position in passageway 9 when trigger sensor 50 detects bill, (iii) drives a release device 42 to shift a guide roller 40 from the contact position to the separated position, (iv) activates a centering device 10 to centralize bill along the longitudinal central axis of passageway 9, (v) drives release device 42 to return guide roller 40 from the separated position to the contact position, and (vi) again drives conveyer device 8 to further inwardly move bill. When bill is inserted into an inlet 7, inlet sensor 13 detects bill to immediately drive conveyer device 8 and center bill on conveyer device 8 for smooth inserting, transporting and centering of bill with the reduced number of structural components of the apparatus.