An erroneous coin insertion preventive mechanism of a banknote handling machine prevents a user from erroneously inserting a coin (or a token) through a banknote slot of the banknote handling machine. When a coin 28 is erroneously inserted through a banknote slot 17, an erroneous coin insertion preventive mechanism 20 holds the rigid coin 28 by three points of a front end contact part 29 and a rear lower surface contact part 31 formed by a horizontal surface 26 and a conveyance path lower surface part 27, and an upper surface intermediate contact part 32 formed by a lower bent part of a descending slope surface of a conveyance path upper surface part 24, thereby preventing the coin 28 from entering an inside of the device from the banknote slot 17. A gap L is provided between the conveyance path upper surface part 24 and the conveyance path lower surface part 27 so that a banknote bundle 33 of a specified number of flexible banknotes thicker than the coin 28 may pass through the gap in bent form.