Fraud prevention mechanism, paper sheet transport device, and paper sheet handling device

A fraud prevention mechanism that is installed on a paper sheet transport route to prevent a fraudulent act on a paper sheet, comprising:

• an opening/closing member that allows passage of the paper sheet when in an initial rotational posture, and that blocks passage of the paper sheet when in a non-initial rotational posture out of the initial rotational posture;
• a rotary member that rotates integrally with the opening/closing member;
• a driving member for opening/closing member driving, that is arranged to oppose the rotary member and that is axially supported to be capable of relatively rotating with respect to the rotary member;
• and
• a drive transmission mechanism that transmits a drive force from the driving member to the rotary member, wherein
• the drive transmission mechanism includes a driven piece provided on the rotary member, and a driving piece that is provided on the driving member and that rotationally drives the rotary member by pressing the driven piece in a course of relatively rotationally moving with respect to the driven piece,
• a circumferential backlash for allowing rotation of the driven piece with respect to the driving piece configured to limit rotation between the driven piece and the driving piece, and
• an angle of the opening/closing member in the non-initial rotational posture, and a value of the circumferential backlash are set to enable prevention of the opening/closing member from being rotated to transition to the initial rotational posture by an operation from outside while the opening/closing member is stopped in the non-initial rotational posture.