To provide a paper loading amount detection mechanism capable of changing full detection timing of paper ejected to a paper ejection part according to needs, and adjusting a paper loading amount to curled paper.

In a paper loading amount detection mechanism for providing swingably an actuator 20 in a paper ejection tray (paper ejection part) from which paper is ejected, and bringing a tip part of the actuator 20 into contact with paper on the top level loaded on the paper ejection tray to detect a loading amount of paper, the length of the actuator 20 is adjustable. For example, a separate adjustment member 20B is screwed into the tip part of the actuator 20, and the adjustment member 20B is rotated to adjust the length of the actuator 20. In addition, a scale 23 showing a length adjustment amount is attached to the actuator 20. Further, a spring (elastic member) 22 is provided at an intermediate part in a longitudinal direction of the actuator 20.