Medium stacking device

A medium stacking device on which a medium ejected from a processing device in an ejection direction is stacked, the device comprising:

• a stacking portion that stacks the medium by a support surface extending in the ejection direction and supporting a part of the medium;
• a pressing portion that presses the medium supported by the support surface from above;
• and
• an upper unit that holds the pressing portion and is displaceable between a first open state and a second open state in which the pressing portion is separated from the support surface and a closed state in which the pressing portion is moved closer to face the support surface, wherein the upper unit has an arm including a convex portion, supported by the stacking portion, and configured to maintain the first open state and the second open state,
• the stacking portion has a cam groove in which a path that receives and guides the convex portion is formed, through which the convex portion moves when the upper unit is displaced between the first open state and second open state and the closed state,
• the cam groove is provided with a first concave portion that is entered by the convex portion, supports the entering convex portion from below, and maintains the upper unit in the first open state, and a second concave portion that maintains the upper unit in the second open state at a position lower than that in the first concave portion, and
• the second concave portion has higher acceptability than the first concave portion with respect to an impact from the convex portion.